As filed with the Securities and Exchange Commission on October 23, 2002

Registration Nos. 333-99019
333-99019-01

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

AMENDMENT NO. 3

TO

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

(Addresses, including zip code, and telephone numbers, including area code, of registrants' principal executive offices)

CT Corporation System
1633 Broadway, 30th Floor
New York, New York 10019
(800) 624-0909
(Name, address, including zip code, and telephone number, including area code, of registrants' agent for service)

Copies to:

Approximate date of commencement of proposed sale to the public:
As soon as practicable after the effective date of this registration statement.

        If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 of the Securities Act of 1933, check the following box. / /

        If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. / /

        If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. / /

        If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. / /

        If the delivery of the prospectus is expected to be made pursuant to Rule 434 under the Securities Act, check the following box. / /

        The registrants hereby amend this registration statement on such date or dates as may be necessary to delay its effective date until the registrants shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, or until this registration statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

Subject to Completion. Dated October 23, 2002.

The information in this preliminary prospectus is not complete and may be changed. These securities may not be sold until the registration statement filed with the Securities and Exchange Commission is effective. This preliminary prospectus is not an offer to sell nor does it seek an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

5,000,000 Units

Platinum Underwriters Holdings, Ltd.

Equity Security Units

        This is an offering of equity security units of Platinum Underwriters Holdings, Ltd. Each equity security unit has a stated amount of $25 and will initially consist of (a) a contract pursuant to which you agree to purchase, for $25, Common Shares of Platinum Holdings on                    , 2005 and (b) a 1/40, or 2.5%, ownership interest in a senior note of its subsidiary, Platinum Underwriters Finance, Inc., with a principal amount of $1,000. The ownership interest in the senior note will initially be held as a component of your unit and be pledged to secure your obligation to purchase Common Shares of Platinum Holdings under the related purchase contract. The senior notes will be guaranteed by Platinum Holdings on a senior, unsecured basis.

        Platinum Holdings will make quarterly contract adjustment payments to you under the purchase contract at the annual rate of        % of the stated amount of $25 per purchase contract. In addition, Platinum Finance will make quarterly interest payments on the senior notes at the initial annual rate of        %. Platinum Holdings has the right to defer the contract adjustment payments on the purchase contracts, but Platinum Finance does not have the right to defer the interest payments on the senior notes. The interest rate on the senior notes will be reset, and the senior notes remarketed. The senior notes are unsecured and rank equally with all of Platinum Finance's other unsecured senior indebtedness. The units will be sold initially by the underwriters in a minimum number of 40 units.

        Prior to this offering and the concurrent initial public offering of Common Shares of Platinum Holdings, there has been no public market for the units or Platinum Holdings' Common Shares.

        In addition to offering these units, Platinum Holdings is concurrently offering 30,040,000 of its Common Shares, plus up to an additional 4,506,000 Common Shares if the underwriters for that offering exercise their option to purchase additional Common Shares. The completion of this offering of equity security units is subject to the completion of the initial public offering of Common Shares of Platinum Holdings.

        The normal units and the Common Shares that will be issued in the concurrent initial public offering have been approved for listing on the New York Stock Exchange, subject to notice of issuance, under the symbols "PTP Pr M" and "PTP", respectively.

        Immediately after this offering, public shareholders, The St. Paul Companies, Inc. and RenaissanceRe Holdings Ltd. will own 75.1%, 15.0% and 9.9% of the outstanding Common Shares, respectively, assuming no exercise by the underwriters, St. Paul or RenaissanceRe of their options to purchase additional Common Shares in connection with the concurrent initial public offering.

        See "Risk Factors" beginning on page 31 to read about certain factors you should consider before buying units.

        Neither the Securities and Exchange Commission nor any other regulatory body has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

        The initial public offering price set forth above does not include accumulated contract adjustment payments and accrued interest, if any. Contract adjustment payments on the purchase contracts and interest on the senior notes will accrue from the date of original issuance of the units, expected to be                          , 2002.

        To the extent that the underwriters sell more than 5,000,000 units, the underwriters have the option to purchase, not later than 13 days after the initial issuance of the units, up to an additional 750,000 units from Platinum Holdings at the initial public offering price less the underwriting discount.

        The underwriters expect to deliver the units against payment in New York, New York on                          , 2002.

Prospectus dated                            , 2002.

PROSPECTUS SUMMARY

        Platinum Underwriters Holdings, Ltd. is a newly formed company that will conduct its business through three operating subsidiaries, Platinum Underwriters Reinsurance, Inc. ("Platinum US"), Platinum Re (UK) Limited ("Platinum UK") and Platinum Underwriters Bermuda, Ltd. ("Platinum Bermuda"). Platinum UK and Platinum Bermuda are newly formed companies, while Platinum US has been in existence since 1995 and is an inactive, wholly owned subsidiary of The St. Paul Companies, Inc. Platinum UK is, and upon completion of this offering, Platinum US will be, owned through Platinum Regency Holdings ("Platinum Ireland"), a newly formed and wholly owned intermediate Irish holding subsidiary of Platinum Underwriters Holdings, Ltd. Platinum US will be owned directly by Platinum Underwriters Finance, Inc. ("Platinum Finance"), a newly formed Delaware corporation, which, upon completion of this offering, will be a wholly owned subsidiary of Platinum Ireland.

        The "Company", "Platinum", "we", "us" and "our" refer to Platinum Underwriters Holdings, Ltd.'s consolidated operations, including Platinum US, unless the context otherwise indicates. "Platinum Holdings" refers solely to Platinum Underwriters Holdings, Ltd. Concurrent with the completion of this offering, St. Paul will contribute to Platinum between $121 million and $126 million in cash, which we refer to as the "Cash Contribution." The St. Paul Companies and its subsidiaries will also contribute to Platinum substantially all of their continuing reinsurance business and related assets, including all of the outstanding capital stock of Platinum US, referred to herein as the "Transferred Business," having a net tangible book value of approximately $11 million as of June 30, 2002 (after reflecting a dividend of $15 million to be paid, prior to the completion of the Equity Public Offering, to United States Fidelity and Guaranty Company, the current parent of Platinum US). Reinsurance is an arrangement in which a reinsurance company indemnifies an insurer or other reinsurer, which is referred to as a "ceding company" or "cedent", against all or a portion of the insurance or reinsurance risks underwritten by the ceding company under one or more policies. "St. Paul" refers to The St. Paul Companies, Inc., which is sponsoring our formation, and, unless the context otherwise requires, its subsidiaries. "St. Paul Re" refers to the reinsurance segment of St. Paul prior to this offering, which includes the continuing business and related assets being transferred to Platinum upon completion of this offering as well as the reinsurance business that will remain with St. Paul after this offering and not be renewed and will thereafter expire when claims are ultimately resolved, which is referred to as the "run-off."

        We intend to commence our property and casualty reinsurance business operations, whereby we indemnify insurers and other reinsurers against all or a portion of their insurance or reinsurance risks for property loss and related damage and negligence resulting in bodily injury or property damage, upon completion of this offering of equity security units, which we refer to as the "ESU Offering." Concurrently with this offering, we will offer 30,040,000 Common Shares by means of a separate prospectus, plus up to an additional 4,506,000 Common Shares if the underwriters' option to purchase additional Common Shares is exercised in full. We refer to this offering as the "Equity Public Offering." The closing of each offering is conditioned on the concurrent closing of the other offering.

        Concurrently with the completion of the Equity Public Offering, St. Paul will make the Cash Contribution and contribute the Transferred Business to us in exchange for our issuance to St. Paul, on a private placement basis, of 6,000,000 Common Shares and a ten-year option, referred to as the "St. Paul Option", which will entitle St. Paul to buy from us up to 6,000,000 additional Common Shares at a price per share equal to 120% of the initial public offering price. St. Paul will own 15.0% of Platinum Holdings' outstanding Common Shares following the Equity Public Offering, the St. Paul Investment and the RenaissanceRe Investment (each as defined below), which Common Shares will be limited to 9.9% of the voting power of the outstanding Common Shares. If the underwriters exercise their option to purchase additional Common Shares in the Equity Public Offering, St. Paul

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has the option to purchase, at a price per share equal to the initial public offering price, less the underwriting discount, as many additional Common Shares as are required in order for it to retain its 15.0% interest (a maximum of 900,000 additional Common Shares). In this prospectus, we refer to our issuance to St. Paul of the 15.0% interest in our Common Shares and the St. Paul Option in exchange for the Cash Contribution and the Transferred Business as the "St. Paul Investment."

        Also, concurrently with the completion of the Equity Public Offering, RenaissanceRe Holdings Ltd. (including its subsidiaries, unless the context otherwise requires "RenaissanceRe"), a Bermuda company that provides reinsurance and insurance coverage, will purchase from us in a private placement, at a price per share equal to the initial public offering price, less the underwriting discount, 3,960,000 Common Shares, or 9.9% of the Common Shares outstanding upon completion of the Equity Public Offering, the St. Paul Investment and the RenaissanceRe Investment (as defined below). If the underwriters exercise their option to purchase additional Common Shares in the Equity Public Offering, RenaissanceRe has the option to purchase, at a price per share equal to the initial public offering price, less the underwriting discount, as many additional Common Shares as are required in order for it to retain its 9.9% interest (a maximum of 594,000 Common Shares). As additional consideration, RenaissanceRe will receive a ten-year option, referred to as the "RenaissanceRe Option", to purchase up to an additional 2,500,000 Common Shares at a price per share equal to 120% of the initial public offering price. In this prospectus, we refer to this private placement as the "RenaissanceRe Investment." The closing of this private placement to RenaissanceRe is conditioned on the completion of the Equity Public Offering, the ESU Offering and the St. Paul Investment.

        We will have a total capitalization of between approximately $955 million (assuming an initial public offering price of $22.00 per Common Share, a Cash Contribution of $121 million and no exercise of the underwriters', St. Paul's or RenaissanceRe's options to purchase additional Common Shares or the underwriters' option to purchase additional equity security units) and approximately $1,142 million (assuming an initial public offering price of $23.00 per Common Share, a Cash Contribution of $126 million and full exercise of the underwriters', St. Paul's and RenaissanceRe's options to purchase additional Common Shares in connection with the Equity Public Offering and the underwriters' option to purchase additional equity security units), upon completion of the Equity Public Offering, the ESU Offering, the St. Paul Investment and the RenaissanceRe Investment. The determination of the amount of the Cash Contribution will be made when the terms of the Equity Public Offering are finally determined. The pro forma net tangible book value per Common Share following the Equity Public Offering, the ESU Offering, the St. Paul Investment and the RenaissanceRe Investment will be $21.24 per share based on an assumed initial public offering price of $22.50 per Common Share (the mid-point of the range at which Platinum Holdings proposes to offer the Common Shares) and a Cash Contribution of $123 million (the mid-point of the $121 million to $126 million range of the Cash Contribution), assuming no exercise of the underwriters' options to purchase additional Common Shares or the underwriters' option to purchase additional equity security units and without giving effect to the settlement of the purchase contracts included in the equity security units.

        In this prospectus, amounts are expressed in U.S. dollars and the financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America ("U.S. GAAP"), except as otherwise indicated.

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The Company

General

        Our objective is to provide property and casualty reinsurance coverages to a diverse clientele of insurers and select reinsurers on a worldwide basis. We will operate principally by using reinsurance brokers to market our products and principally as a lead reinsurer on treaty reinsurance business. In treaty reinsurance, a reinsurer accepts a specified portion of a category of risks insured by a ceding insurer or reinsurer. A substantial majority of our business will be written as excess-of-loss reinsurance, which indemnifies the reinsured against all or a specified portion of loss above a specified amount. We intend to organize our worldwide reinsurance business around three operating segments:

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Global Property and Marine. The Global Property and Marine operating segment will include principally property reinsurance coverages and marine reinsurance coverages. Marine reinsurance coverages include all types of marine vessels and related warehouses and liabilities. We intend to focus our underwriting activities primarily on catastrophe excess-of-loss and per risk excess-of-loss contracts. Catastrophes are events such as hurricanes and earthquakes that produce pre-tax losses before reinsurance which, in our definition, are in excess of $10 million to us or $1 billion to the insurance industry, and per risk excess-of-loss contracts cover losses in excess of a specified level on a single risk, rather than aggregate losses for all covered risks. We intend to write other types of property reinsurance as well, including selected property proportional reinsurance, where we will share a proportional part of the original premiums and losses of the reinsured. This segment generated $315 million, or 22.8%, of Platinum's 2001 pro forma net premiums written, which are gross written premiums less premiums ceded to reinsurers.



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Global Casualty. The Global Casualty operating segment will include principally general and automobile liability, professional liability, workers' compensation, accident and health coverages and casualty clash (casualty clash covers losses arising from a single set of circumstances covered by more than one cedent's insurance policy or multiple claimants on one policy). We intend to focus our underwriting activities primarily on excess-of-loss reinsurance coverages. This segment generated $592 million, or 42.8%, of Platinum's 2001 pro forma net premiums written.



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Finite Risk. The Finite Risk operating segment, which writes policies under which our aggregate risk and return are generally capped at a finite amount, will include principally non-traditional reinsurance treaties, including multi-year excess-of-loss (in which the cedent funds the agreed level of loss activity over a multi-year period, and the reinsurer charges an additional amount to provide a profit margin and to cover its costs and the risk that losses are worse than the agreed level), aggregate stop loss (which provides protection from losses arising from a wide range of circumstances in excess of an aggregate specified level), finite quota share (in which the reinsurer's losses and profit potential are capped at specified amounts), loss portfolio transfer (which typically transfers to the reinsurer all liabilities for incurred losses, subject to an aggregate loss limit specified in the contract), and adverse loss development contracts (which typically provide reinsurance coverage for losses in excess of the carried loss reserves of the ceding company at the transaction date). We intend to provide clients, either directly or through brokers, with customized solutions for their risk management and other financial management needs. We intend to focus our finite risk underwriting activities primarily on multi-year excess-of-loss and aggregate stop loss reinsurance treaties. Coverage classes within these products will primarily include property, casualty and marine exposures. This segment generated $475 million, or 34.4%, of Platinum's 2001 pro forma net premiums written.

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        In addition, we may write other property and casualty reinsurance on an opportunistic basis. For a discussion of the basis on which pro forma net premiums written were determined, see
"—Selected Pro Forma Financial Information and Operating Data" below.

Background and the Transferred Business

        St. Paul and its subsidiaries constitute one of the oldest insurance organizations in the United States, dating back to 1853. Through its division St. Paul Re, St. Paul has been engaged in the reinsurance business since 1983. In December of 2001, in an effort to enhance the profitability of its reinsurance business, St. Paul decided to narrow the product focus of its reinsurance operations and to exit certain lines of that business. As part of this effort, St. Paul Re reduced its anticipated 2002 exposure and expenses by exiting unprofitable lines of business and reducing the number of reinsurance branch offices outside the United States. The narrowing of reinsurance product lines included exiting aviation, bond and credit reinsurance coverages, as well as certain financial risk and capital markets lines. International branch office closings included Munich, Brussels, Hong Kong, Sydney and Singapore. In addition to curtailing various reinsurance operations, St. Paul's management decided that its reinsurance business and its primary insurance business should ideally operate as separate entities because of their different risk profiles and business characteristics.

        Accordingly, St. Paul determined to sponsor the formation of Platinum Holdings and its subsidiaries. Contingent upon the completion of the Equity Public Offering, St. Paul will contribute to us the Cash Contribution and the Transferred Business through the arrangements described below:

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Cash Contribution. At the completion of the Equity Public Offering, St. Paul will make the Cash Contribution in the amount of between $121 million and $126 million. The determination of the amount of the Cash Contribution will be made when the terms of the Equity Public Offering are finally determined. An assumed Cash Contribution of $123 million will result in a pro forma net tangible book value per Common Share of $21.24 following the Equity Public Offering, the ESU Offering, the St. Paul Investment and the RenaissanceRe Investment based on an assumed initial public offering price of $22.50 per Common Share (the midpoint of the range at which Platinum Holdings proposes to offer the Common Shares) and assuming no exercise of the underwriters', St. Paul's or RenaissanceRe's options to purchase additional Common Shares in connection with the Equity Public Offering or the underwriters' option to purchase additional equity security units. Cash Contributions of $121 million and $126 million will result in net tangible book values of $20.76 and $21.71 per Common Share, respectively, assuming an initial public offering price of $22.00 and $23.00, respectively, and no exercise of the underwriters' options to purchase additional Common Shares or additional equity security units and without giving effect to the settlement of the purchase contracts included in the equity security units.



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Renewal Opportunities and Commitments. We will be acquiring from St. Paul Re its existing customer lists and the right to seek to renew substantially all of St. Paul Re's continuing reinsurance contracts. We also will assume commitments, if any, of St. Paul Re to offer reinsurance coverages in the future.



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Assumed Reinsurance Contracts. Through 100% quota share retrocession agreements (the "Quota Share Retrocession Agreements"), we will reinsure substantially all of the reinsurance contracts entered into by St. Paul Re on or after January 1, 2002, which we refer to as the "Assumed Reinsurance Contracts". St. Paul Re will retain all of its reinsurance exposure not being transferred to us and will administer the associated run-off. Consequently, we will not assume any underwriting exposure with respect to reinsurance contracts entered into by

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St. Paul prior to January 1, 2002, except as noted below with respect to finite reinsurance. St. Paul will also retain all liabilities relating to the flooding in Europe in August 2002 and an intermediate layer of liability for named storms (which are any tropical cyclones assigned a name by the National Hurricane Center) in existence at the time of completion of the Equity Public Offering which cause insured damage within ten days of such time, as described herein. We will receive as consideration cash and other assets in an amount equal to the aggregate of all applicable loss reserves (excluding reserves relating to liabilities retained by St. Paul), allocated loss adjustment expense reserves (which are reserves relating to the expense incurred in settling claims), other reserves related to non-traditional reinsurance treaties, ceding commission reserves (which are reserves relating to commissions payable to ceding insurers) and unearned premium reserves (which are reserves equal to the difference between premiums written and premiums earned) subject to agreed upon adjustments, net of ceding commissions under the Quota Share Retrocession Agreements as of the transfer date (which is 12:01 a.m. on the day immediately following the date of the completion of the Equity Public Offering). Underwriting gain or loss with respect to the Assumed Reinsurance Contracts for the period from January 1, 2002 to the transfer date will be retained by St. Paul.

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The terms of the Quota Share Retrocession Agreements provide, with limited exceptions, that retrocessional reinsurance, which is reinsurance obtained by a reinsurer to insure against all or a portion of its reinsurance written, purchased by St. Paul Re shall be for our expense and shall inure to our benefit in respect of the Assumed Reinsurance Contracts, providing us with remaining retrocessional reinsurance coverage for such contracts through 2002 or the earlier termination or expiration of the various retrocession agreements. We will bear all the risk associated with non-payment by third-party retrocessionaires under such retrocessional reinsurance. All the Quota Share Retrocession Agreements will take effect as of 12:01 a.m. on the day immediately following the date of the completion of the Equity Public Offering. Accordingly, while St. Paul will be contractually committed to effect the transfer, the effective time of the transfer of the Assumed Reinsurance Contracts will occur after the sale to investors of Common Shares in the Equity Public Offering.



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In the case of business written in the United States and the United Kingdom, we will have the right to underwrite specified reinsurance business on behalf of St. Paul for a period of one year following the completion of the Equity Public Offering in cases where we are unable to underwrite that business ourselves because, despite using our reasonable best efforts, we have not obtained the necessary regulatory license or approval to do so or we have not yet been approved as a reinsurer by the cedent, and we will reinsure such business pursuant to the Quota Share Retrocession Agreements or, following receipt by Platinum UK of a license from the Financial Services Authority (the "FSA"), may reinsure all or a part of such business pursuant to a quota share retrocession agreement to be entered into between Platinum UK and St. Paul Re UK. This will allow us to participate in reinsurance business which is bound after the completion of the Equity Public Offering without any delay occasioned by the start-up of our operations, including the lack of required licenses, and facilitate the transition of St. Paul Re's business to us.



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For a period of three years following the completion of the Equity Public Offering, we will underwrite on behalf of St. Paul, with the consent of St. Paul, renewals of in-force contracts of finite reinsurance. St. Paul will retrocede to us 100% of the unpaid and future losses under currently in-force contracts, and we will have the option to reinsure losses under certain renewed contracts and will be required to offer to reinsure losses

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under other renewed contracts, for a fair market retrocession premium pursuant to the Quota Share Retrocession Agreements. Under the Quota Share Retrocession Agreements, a portion of future premiums will be applied to settle balances related to prior year experience for the benefit of St. Paul. St. Paul will have an option to renew this arrangement with us for a subsequent period of two years. In the United Kingdom, this arrangement will be limited to finite treaties which St. Paul Re has entered into with a small number of identified cedents and any further finite treaties which may be entered into on behalf of St. Paul Re UK prior to the first anniversary of the completion of the Equity Public Offering.

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Related Assets. We will be acquiring from St. Paul tangible and intangible assets relating to the continuing businesses being transferred to us, including furniture and equipment, systems and software, assignments of leases, licenses and other assets, as well as all of the outstanding capital stock of Platinum US.



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Employees. Upon or following the completion of the Equity Public Offering, we expect to employ approximately 150 employees previously employed by St. Paul Re.

        St. Paul has agreed with us that, subject to certain exceptions, for a period of two years following the completion of the Equity Public Offering, it will not offer reinsurance of the type covered by the Assumed Reinsurance Contracts and for which we have acquired renewal rights or hire certain of our employees.

        For a discussion of the share ownership interests St. Paul will obtain for its contribution of the Transferred Business, see "—St. Paul's Share Ownership" below.

Our Organization

        The following chart summarizes our corporate structure upon completion of the transactions contemplated by this prospectus. Our operating business will be conducted by Platinum US, Platinum UK and Platinum Bermuda. Platinum Bermuda expects to reinsure up to approximately 70% of Platinum US's reinsurance business, excluding business subject to the Quota Share Retrocession Agreements, written after the completion of the Equity Public Offering, and we are seeking consent from the FSA for Platinum Bermuda to reinsure up to approximately 55% of Platinum UK's reinsurance business, excluding business subject to the Quota Share Retrocession Agreements, written after the Equity Public Offering; however, such consent may not be granted. St. Paul will continue to write reinsurance in the United Kingdom and reinsure it 100% to us for up to one year following the completion of the Equity Public Offering. For a discussion of potential future limits on the portion of the reinsurance written by Platinum UK after the completion of the Equity Public Offering which can be reinsured to Platinum Bermuda, see "Business—Our Business—Regulation—U.K. Regulation—Proposed Limits on Concentration of Reinsurance Exposures."

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Management and Directors

        We have assembled a senior management team of experienced insurance industry professionals, whose backgrounds include underwriting and marketing property and casualty reinsurance worldwide. Steven H. Newman, who is the Chairman of Platinum Holdings' Board of Directors, Jerome T. Fadden, who is Platinum Holdings' President and Chief Executive Officer, William A. Robbie, who is Chief Financial Officer of Platinum Holdings, Michael E. Lombardozzi, who is General Counsel of Platinum Holdings, Michael D. Price, who will be President and Chief Underwriting Officer of Platinum US, and Neal J. Schmidt, who will be Chief Actuary of Platinum US, in each case upon completion of the Equity Public Offering, have extensive experience in the global property and casualty reinsurance industry. The new senior management team intends to initiate a number of actions to improve the underwriting performance and profitability of the Company. These actions are described more fully under "—Platinum's Strategy" below.

        Our Board of Directors consists of seven members: Mr. Newman; Mr. Fadden; Jay S. Fishman, Chairman of the Board of Directors and Chief Executive Officer of The St. Paul Companies, Inc.; H. Furlong Baldwin, Chairman of Mercantile Bankshares Corporation; Jonathan F. Bank, Senior Vice President of Tawa Associates Ltd.; Dan R. Carmichael, President and Chief Executive Officer of Ohio Casualty Corporation; and Peter T. Pruitt, retired Chairman of Willis Re Inc.

Our Competitive Strengths

        We believe that with our experienced management team, unencumbered capital base and the long-term potential of the business and assets of St. Paul Re obtained from St. Paul, we will have the benefits of being both an established business and a new market entrant. As a well-capitalized, focused reinsurer, we believe we will be able to expand our relationships with clients of St. Paul Re as well as new clients to a greater extent than if our operations were part of a multi-line insurer such as St. Paul.

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        We intend to focus our initial marketing efforts on those brokers and their clients with which St. Paul Re has established business relationships. We feel that the existing portfolio of business generated by St. Paul Re represents a valuable asset given the renewal nature of the reinsurance industry and the importance of continuity of relationships. We believe that the market perceptions and reputation established by St. Paul Re with respect to service and responsiveness will benefit us in light of the transfer of personnel and underwriting activities from St. Paul Re to us.

Platinum's Strategy

        Our goal is to achieve superior long-term returns for our shareholders, while establishing Platinum as a conservative risk manager and market leader in certain classes of property and casualty reinsurance.

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Build our future on a strong foundation. We will commence operations with the benefit of the Transferred Business:



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Renewal Rights and Assumed Reinsurance Contracts. Our initial portfolio will contain a diversity of business that would normally take many years to develop. We will be acquiring St. Paul Re's existing customer lists and the right to seek to renew its continuing in-force reinsurance contracts, which produced 2001 pro forma net premiums written of approximately $1.4 billion.



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Fully operational infrastructure. We will select experienced employees from the skilled St. Paul Re employee base. These employees have broker and ceding company relationships and underwriting pricing and claims experience that will allow us to be fully staffed and operational in key underwriting and support functions.




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Add new executive leadership to existing talent. In order to take full advantage of the historical strengths of St. Paul Re, we have significantly strengthened our senior management team with the addition of Mr. Newman and Mr. Fadden. Mr. Newman and Mr. Fadden have extensive experience in leading publicly traded reinsurance companies and intend to implement a number of initiatives to create a more focused and more profitable reinsurance business.



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Focus on profitability, not market share. Our new management team intends to pursue a strategy that emphasizes underwriting discipline and profitability over market share. Key elements of this strategy will be prudent risk selection, appropriate pricing through strict underwriting discipline and increasing our writings of lines of business, which we believe will contribute to our long-term profitability.



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Exercise disciplined underwriting and risk management. We intend to exercise risk management discipline by (i) maintaining a diverse spread of risk in our book of business across products and geographic zones, (ii) focusing on excess-of-loss contracts as opposed to proportional contracts and (iii) reducing our aggregate catastrophe exposure.



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Operate a lean and expense-focused underwriting business. We believe a lean underwriting culture will support our focus on profitability and allow us to be more responsive to changing market conditions. We intend to keep our headcount low and maintain a limited number of offices. In addition, we expect to originate most of our business from brokers, rather than directly from ceding companies or cedents, which are insurance companies seeking reinsurance coverages, which we believe will keep our expenses low.




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Grow our business by leveraging our global platform. We intend to operate in all three of the world's leading reinsurance markets with offices in New York, London and Bermuda.

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St. Paul Re has conducted authorized reinsurance activities in the United States and London for many years. Our new Bermuda subsidiary will provide us with both a new market in which to write reinsurance and the flexibility to provide reinsurance products that are best facilitated by an offshore company.

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Operate from a position of financial strength. As a newly formed company, our initial capital position is unencumbered by any development of loss reserves for business written prior to January 1, 2002, which are reserves established to reflect estimated cost of loss payments that ultimately will be required to be paid. Upon completion of the Equity Public Offering, the ESU Offering, the St. Paul Investment and the RenaissanceRe Investment, we expect to have a total capitalization of between approximately $955 million (assuming an initial public offering price of $22.00, a Cash Contribution of $121 million and no exercise of the underwriters', St. Paul's or RenaissanceRe's options to purchase additional Common Shares or the underwriters' option to purchase additional equity security units) and approximately $1,142 million (assuming an initial public offering price of $23.00, a Cash Contribution of $126 million and full exercise of the underwriters', St. Paul's and RenaissanceRe's options to purchase additional Common Shares in connection with the Equity Public Offering and the underwriters' option to purchase additional equity security units). Our investment strategy will focus on security and stability in our investment portfolio by maintaining a diversified portfolio that will consist primarily of investment grade fixed-income securities.

Recent Industry Trends

        After an extended period of increased competition and eroding premiums, the reinsurance markets began experiencing improvements in rates, terms and conditions in the first quarter of 2000. These improvements continued in 2001 and were accelerated by the terrorist attack of September 11, 2001, which resulted in a range of estimated property and casualty insurance losses to the insurance industry of between $30 billion and $35 billion, the largest estimated catastrophe losses ever experienced by the industry. We believe property and other reinsurance premiums have often risen in the aftermath of significant catastrophe losses. As claims are reserved, industry surplus is depleted and the industry's capacity to write new business diminishes. At the same time, there appears to be heightened awareness that commercial properties are exposed to a variety of risks. We believe that market trends similar to those that have occurred in past cycles are developing in the current environment. With respect to January, April and July 2002 renewals, St. Paul Re experienced substantial rate increases, generally ranging from 20% to 50% depending on the line of business. We believe that the current imbalance between the increased demand for property-related insurance and reinsurance and the reduced supply of this type of coverage will continue at least for the immediate future.

St. Paul's Share Ownership

        St. Paul has determined that the efficiency, profitability and competitive position of its reinsurance operations can be maximized by separating them from St. Paul's primary insurance operations. Despite the separation of the two businesses, St. Paul will continue to participate in future financial results of the reinsurance business through its ownership of Common Shares as a result of the St. Paul Investment.

        In return for the Cash Contribution and the Transferred Business, we will issue 6,000,000 Common Shares to St. Paul (so that St. Paul will own 15.0% of our outstanding Common Shares following the Equity Public Offering, the St. Paul Investment and the RenaissanceRe Investment) and the St. Paul Option. St. Paul's Common Shares will be limited to 9.9% of the voting power of the outstanding Common Shares. If the underwriters exercise their option to purchase additional

9

Common Shares in the Equity Public Offering, St. Paul will have the option to purchase additional Common Shares at a price per share equal to the initial public offering price less the underwriting discount in order for it to retain its 15.0% interest. In addition, we will grant St. Paul the St. Paul Option, which is a ten-year option to purchase up to 6,000,000 Common Shares at 120% of the initial public offering price for the Equity Public Offering. Exercise of such option by St. Paul in full immediately after completion of the Equity Public Offering, the St. Paul Investment and the RenaissanceRe Investment would increase its percentage interest in our Common Shares to approximately 26.1%, assuming no exercise of the underwriters', St. Paul's or RenaissanceRe's options to purchase additional Common Shares in connection with the Equity Public Offering or of the RenaissanceRe Option. However, St. Paul has agreed with us that, prior to any exercise of the St. Paul Option, it will, if necessary, dispose of a sufficient number of Common Shares so that, immediately after exercise of the St. Paul Option, St. Paul would not be a "United States 25% Shareholder" as defined under "Description of Platinum Holdings' Common Shares—Restrictions on Transfers." St. Paul has informed us that it currently intends to continue its share ownership in Platinum Holdings for the foreseeable future.

RenaissanceRe's Share Ownership and Business Arrangements

        In connection with the RenaissanceRe Investment, we will issue to RenaissanceRe 3,960,000 Common Shares (so that RenaissanceRe will own 9.9% of our outstanding Common Shares following the Equity Public Offering, the St. Paul Investment and the RenaissanceRe Investment) and the RenaissanceRe Option. If the underwriters exercise their option to purchase additional Common Shares in the Equity Public Offering, RenaissanceRe will have the option to purchase additional Common Shares at a price per share equal to the initial public offering price less the underwriting discount, in order for it to retain its 9.9% interest. In addition, we will grant RenaissanceRe the RenaissanceRe Option, which is a ten-year option to purchase up to 2,500,000 Common Shares at 120% of the initial public offering price of the Equity Public Offering. Exercise of such option by RenaissanceRe in full immediately after completion of the Equity Public Offering, the St. Paul Investment and the RenaissanceRe Investment would increase its percentage interest in Platinum Holdings' Common Shares to approximately 15.2%, assuming no exercise of the underwriters', St. Paul's or RenaissanceRe's options to purchase additional Common Shares in connection with the Equity Public Offering or of the St. Paul Option. RenaissanceRe has agreed with us that, prior to any exercise of the RenaissanceRe Option, it will, if necessary, dispose of a sufficient number of Common Shares so that, immediately after exercise of the RenaissanceRe Option, RenaissanceRe would not beneficially own more than 19.9% of our outstanding voting securities (or up to 24.9% with our approval). See "Description of Platinum Holdings' Common Shares—Restrictions on Transfers." RenaissanceRe has informed us that it currently intends to continue its share ownership in Platinum Holdings for the foreseeable future.

        We have entered into an investment agreement with St. Paul and RenaissanceRe, which provides RenaissanceRe with, among other things, the right to nominate one director to our Board of Directors and, in addition, to designate a non-voting representative to attend our Board of Directors meetings, subject to certain conditions.

        We also will enter into an agreement, which we refer to as the "Services and Capacity Reservation Agreement" in this prospectus, with RenaissanceRe, pursuant to which in exchange for certain payments by us to RenaissanceRe, RenaissanceRe will provide services to us in connection with the reviewing and repositioning of our property catastrophe book of business for a period of five years. These services will include assisting us in measuring risk and managing our aggregate catastrophe exposures. In addition, we expect that we and RenaissanceRe may refer business to each other, to be accepted in the discretion of the party receiving the referral, and that compensation will be paid for referral business at negotiated rates.

        RenaissanceRe is a Bermuda company principally engaged, through its operating subsidiaries, in providing reinsurance and insurance coverage that is subject to the risk of natural and man-made catastrophes. For a further discussion of our relationship with RenaissanceRe, see "Certain Relationships and Related Transactions—The RenaissanceRe Investment."

Principal Executive Offices

        Platinum Holdings was organized on April 19, 2002 as a company limited by shares under Bermuda law. Platinum Holdings' principal executive offices are located at Clarendon House, 2 Church Street, Hamilton HM 11, Bermuda. Its telephone number is (441) 295-5950.

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The ESU Offering

What are the equity security units?

        Each equity security unit, which we refer to as a "unit", will initially consist of and represent:

        (1) a purchase contract pursuant to which:

•

you will agree to purchase, and Platinum Holdings will agree to sell, for $25, Common Shares on                          , 2005 (the "share purchase date"), the number of which will be determined based on the average trading price of the Common Shares for a period preceding that date, calculated in the manner described below; and

•

Platinum Holdings will pay you contract adjustment payments on a quarterly basis at the annual rate of    % of the stated amount of $25, subject to its right to defer such payments, as specified below; and

        (2) a 1/40, or 2.5%, ownership interest in a senior note due            , 2007 of Platinum Finance, an indirect, wholly owned subsidiary of Platinum Holdings, with a principal amount of $1,000, on which Platinum Finance will pay interest at the initial annual rate of    % until a successful remarketing of the senior notes and at the reset rate (as described below) thereafter. Interest will be payable quarterly in arrears through and including the share purchase date and, thereafter, semi-annually in arrears. The senior notes will be guaranteed by Platinum Holdings on a senior, unsecured basis.

        The ownership interests in the senior notes that are a component of your units will be owned by you, but will initially be pledged to the collateral agent for the benefit of Platinum Holdings to secure your obligations under the related purchase contracts. We refer in this prospectus to the purchase contracts, together with the pledged ownership interest in the senior notes (or, after a successful remarketing, a tax event redemption or prepayment in full of the senior notes described below, the specified pledged treasury securities), as "normal units."

        Each holder of normal units may elect at any time on or before the second business day prior to the share purchase date (subject to certain exceptions) to withdraw from the pledge the pledged ownership interest in the senior notes (or, after a successful remarketing or tax event redemption described below, the pledged treasury securities) underlying the normal units, thereby creating "stripped units." To create stripped units, the holder must substitute, as pledged securities, specifically identified treasury securities that will pay $25 (the amount due under the purchase contract) per unit on the share purchase date, and the pledged ownership interest in the senior notes or treasury securities will be released from the pledge and delivered to the holder. Holders of stripped units may recreate normal units by re-substituting the senior notes (or, after a successful remarketing or a tax event redemption, the applicable treasury securities) for the treasury securities underlying the stripped units.

        If the senior notes are successfully remarketed or a tax event redemption occurs, in each case as described in this prospectus, the applicable ownership interest in the treasury securities will replace the ownership interest in a senior note as a component of each unit and will be pledged to the collateral agent for the benefit of Platinum Holdings to secure your obligations under the purchase contract.

What are the purchase contracts?

        The purchase contract underlying a unit obligates you to purchase, and Platinum Holdings to sell, for $25, on the share purchase date, a number of newly issued Common Shares equal to the settlement rate described below. The settlement rate will be based on the average trading price of the Common Shares for a period preceding that date, calculated in the manner described below.

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What payments will be made to holders of the units and the senior notes?

        If you hold normal units, Platinum Holdings will pay you quarterly contract adjustment payments on the underlying purchase contracts at the annual rate of     % of the $25 stated amount through and including the share purchase date and Platinum Finance will pay you quarterly interest payments on the ownership interests in senior notes that are pledged in respect of your normal units at the initial annual rate of    % through and including            , 2005, the last quarterly payment date before the share purchase date. On the share purchase date, you will also receive a cash payment in respect of each of your normal units, equal to 1/40, or 2.5%, of the quarterly interest payment payable on the $1,000 principal amount of a senior note at the initial annual rate of    % unless the senior notes shall have been prepaid in full prior to a successful remarketing.

        If you hold stripped units and do not separately hold senior notes, you will receive only the quarterly contract adjustment payments payable by Platinum Holdings at the annual rate of     % of the $25 stated amount.

        The contract adjustment payments on normal and stripped units are subject to Platinum Holdings' deferral right as described below. Platinum Finance is not entitled to defer interest payments on any senior notes, whether held as part of, or separately from, the units.

        If you hold senior notes separately from the units and do not separately hold stripped units, you will receive only the interest payable on the senior notes. The senior notes, whether held separately from or as part of the units, will pay interest at the initial annual rate of            % until the settlement date of a successful remarketing, as described below. If the senior notes are successfully remarketed, the rate of interest payable from the settlement date of the successful remarketing until their maturity on            , 2007 will be the reset rate, which will be a rate established by the remarketing agent that meets the requirements described in this prospectus. If the remarketing agent cannot establish a reset rate on a remarketing date, the remarketing agent will not reset the interest rate on the senior notes and the interest rate will continue to be the initial annual rate of    %, until the remarketing agent, on a later remarketing date prior to the share purchase date, can establish a reset rate meeting the requirements described in this prospectus.

        Both Platinum Finance and Platinum Holdings are holding companies with no operations of their own. Although Platinum Finance will retain a portion of the net proceeds of the offering sufficient to fund the interest payments due on the senior notes payable on or prior to the share purchase date, the ability of Platinum Finance and Platinum Holdings to pay their respective obligations under the senior notes and the guarantee otherwise depends on their ability to obtain cash dividends or other cash payments or obtain loans from their subsidiaries, which are separate and distinct legal entities that will have no obligations to pay any dividends or to lend or advance them funds and which may be restricted from doing so by other financing arrangements, charter provisions or regulatory requirements. Platinum Finance's and Platinum Holdings' obligations under the senior notes and the guarantee will be effectively subordinated to the debt and other obligations of their respective subsidiaries. As of June 30, 2002, on a pro forma basis, Platinum Finance's subsidiaries had no liabilities or obligations that would have effectively ranked senior to the senior notes and Platinum Holdings' subsidiaries had approximately $270 million in liabilities and obligations that would have effectively ranked senior to the guarantees.

What are the payment dates?

        Subject to Platinum Holdings' deferral right in respect of the contract adjustment payments described below, contract adjustment payments will be made quarterly in arrears on each                      ,                       ,                       and                       , commencing on                      2003 and ending on the share purchase date. Interest payments on the senior notes initially will be made quarterly in arrears on each                      ,                       ,                       and                       , commencing

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on                      2003, and, following the share purchase date, semi-annually in arrears on each                      and                       until maturity on                      , 2007.

When can Platinum Holdings and Platinum Finance defer payments?

        Platinum Holdings can defer payment of all or part of the contract adjustment payments on the purchase contracts until no later than the share purchase date. Platinum Holdings will accrue additional contract adjustment payments on any deferred installments of contract adjustment payments at a rate of    % per year until paid, compounded quarterly, to but excluding the share purchase date, unless your purchase contract has been earlier settled or terminated.

        Platinum Finance is not entitled to defer interest payments on the senior notes.

What is the reset rate?

        In order to facilitate the remarketing of the senior notes at the remarketing price described below, the remarketing agent will reset the rate of interest on the senior notes, effective from the settlement date of a successful remarketing until their maturity on            , 2007. The reset rate will be the rate sufficient to cause the then current market value of each outstanding senior note to be equal to at least 100.25% of the remarketing value described below. Resetting the interest rate on the senior notes at this rate is designed to enable the remarketing agent to remarket the senior notes in the remarketing and purchase the necessary treasury securities, the proceeds of which will be applied in settlement of the purchase contracts and to provide funds for the cash payment on the normal units due on the share purchase date.

        The reset rate will be determined by the remarketing agent on the third business day (as defined below) prior to            , 2005, the last quarterly payment date before the share purchase date. If the remarketing agent cannot establish a reset rate meeting these requirements on the remarketing date and, as a result, the senior notes cannot be remarketed as described below, the interest rate will not be reset and will continue to be the initial rate of the senior notes. However, the remarketing agent may thereafter attempt to establish a reset rate meeting these requirements, and the remarketing agent may attempt to remarket the senior notes, on the subsequent dates described below. If a reset rate cannot be established on a given date, the remarketing will not occur on that date. If the remarketing agent fails to remarket the senior notes that form part of normal units by the end of the third business day immediately preceding the share purchase date, Platinum Holdings will exercise its rights as a secured party with respect to such senior notes and, subject to applicable law, may retain the pledged senior notes or sell them in one or more public or private sales to satisfy in full such holder's obligation to purchase Common Shares under the related purchase contracts.

        The reset of the interest rate on the senior notes in connection with a successful remarketing will not change the amount of the cash payment due to holders of normal units on the share purchase date, which, as described above, will be an amount per normal unit equal to 1/40, or 2.5%, of the quarterly interest payment payable on $1,000 principal amount of a senior note at the initial annual rate of            %.

        "Business day" means any day that is not a Saturday, Sunday or day on which banking institutions and trust companies in the State of New York or in the city where the principal corporate trust office of the collateral agent is located or at a place of payment are authorized or required by law, regulation or executive order to close. Platinum Holdings has initially appointed State Street Bank and Trust Company, whose principal corporate trust office is located in Boston, Massachusetts, to act as collateral agent.

        The reset rate may not exceed the maximum rate, if any, permitted by applicable law.

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What is remarketing?

        The remarketing agent will attempt to remarket the senior notes of holders of normal units and will use the proceeds to purchase treasury securities, which the participating holders of normal units will pledge to secure their obligations under the related purchase contracts. Holders of normal units may elect not to participate in any remarketing by following the procedures described below. The cash paid upon maturity of the pledged treasury securities underlying the normal units of such holders will be used to satisfy such holders' obligations to purchase Common Shares on the share purchase date, as well as to provide funds to make the cash payment to holders of normal units due on the share purchase date. This will be one way for holders of normal units to satisfy their obligations to purchase Common Shares under the related purchase contracts. The remarketing agent will attempt to remarket the senior notes that are included in normal units on one or more occasions starting on the remarketing date, which will be the third business day prior to            , 2005 or, if the remarketing agent fails to remarket the senior notes on that date, a later date as described below. As described below, a holder of a senior note in which interests are not held as part of normal units may elect to have the separately held senior note remarketed along with the senior notes in which interests are held as part of the normal units.

        Platinum Holdings and Platinum Finance will enter into a remarketing agreement with a nationally recognized investment banking firm that will act as remarketing agent. It is currently anticipated that Goldman, Sachs & Co. will be the remarketing agent. The remarketing agent will agree to use commercially reasonable best efforts to remarket the senior notes that are included in normal units (or separately held senior notes) that are participating in the remarketing, at a price per senior note equal to at least 100.25% of the remarketing value. The "remarketing value" of a senior note will be equal to the sum of:

        (1) the value at the remarketing date (or any subsequent remarketing date) of such amount of treasury securities that will pay, on or prior to the share purchase date, an amount of cash equal to the interest payment scheduled to be payable on the senior note on that date, assuming for this purpose, even if not true, that the interest rate on the senior notes remains at the initial rate; and

        (2) the value at the remarketing date (or any subsequent remarketing date) of such amount of treasury securities that will pay, on or prior to the share purchase date, an amount of cash equal to the principal amount of the senior note.

        The remarketing agent will use the proceeds from a successful remarketing of the senior notes included in normal units to purchase, in its discretion, the amount and the types of treasury securities described in (1) and (2) above in respect of each such senior note that has been remarketed. The remarketing agent will purchase such treasury securities in open market transactions or at treasury auction and deliver them through the purchase contract agent to the collateral agent to secure the obligations under the related purchase contracts of the holders of the normal units whose senior notes participated in the remarketing. The remarketing agent will deduct out of the proceeds in excess of the remarketing value as a remarketing fee an amount not exceeding 25 basis points (0.25%) of the total proceeds from such remarketing. The remarketing agent will remit the remaining portion of the proceeds, if any, for payment to the holders of the normal units participating in the remarketing.

        A holder of normal units may elect not to participate in any remarketing and, instead, retain the ownership interests in senior notes underlying those normal units by delivering, in respect of each senior note to be retained, the treasury securities having the value described in (1) and (2) above, in the amount and the types specified by the remarketing agent, to the purchase contract agent on the fourth business day prior to the first day of a remarketing period (as defined below) to satisfy its obligations under the related purchase contracts. Whether or not a holder of normal units

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participates in the remarketing, the interest rate on the senior notes in which interests are included in those units will nevertheless be reset if the remarketing is successful.

        Prior to any remarketing, Platinum Finance and Platinum Holdings plan to file and obtain effectiveness of a registration statement if so required under the U.S. federal securities law at the time.

What happens if the remarketing agent does not successfully remarket the senior notes on the remarketing date?

        If the remarketing agent cannot establish a reset rate meeting the requirements described above on the remarketing date and therefore cannot remarket the senior notes participating in the remarketing on the remarketing date at a price per senior note equal to at least 100.25% of the remarketing value, the remarketing agent will attempt to establish a reset rate meeting these requirements on each of the two business days immediately following the initial proposed remarketing date. If the remarketing agent cannot establish a reset rate meeting these requirements on either of those days, it will attempt to establish such a reset rate on each of the three business days immediately preceding            , 2005. If the remarketing agent cannot establish such a reset rate during that period, it will further attempt to establish such a reset rate on the third business day immediately preceding the share purchase date. We refer to each of these periods as a "remarketing period." Any subsequent remarketing will be at a price per senior note equal to at least 100.25% of the remarketing value on the subsequent remarketing date. If the remarketing agent fails to remarket the senior notes underlying the normal units at that price by the end of the third business day immediately preceding the share purchase date, any holder of normal units that has not otherwise settled its purchase contracts in cash on the business day immediately preceding the share purchase date (but without regard to the notice requirements otherwise applicable to cash settlement) will be deemed to have directed Platinum Holdings to retain the securities pledged as collateral in satisfaction of the holder's obligations under the related purchase contracts and Platinum Holdings will exercise its rights as a secured party and may, subject to applicable law, retain or dispose of such securities to satisfy in full such holder's obligation to purchase Platinum Holdings' Common Shares under the related purchase contracts on the share purchase date. In no event will a holder of a purchase contract be liable for any deficiency between such proceeds and the purchase price for the Common Shares under the purchase contract.

If I am not a party to a purchase contract, may I still participate in a remarketing of my senior notes?

        Holders of senior notes in which interests are not included as part of normal units may elect to have their senior notes included in the remarketing in the manner described in "Description of the Equity Security Units—Optional Remarketing." The remarketing agent will use commercially reasonable best efforts to remarket the separately held senior notes included in the remarketing at a price per senior note equal to at least 100.25% of the remarketing value, determined on the same basis as for the other senior notes being remarketed. After deducting as a remarketing fee an amount not exceeding 25 basis points (0.25%) of the total proceeds from such remarketing, the remaining portion of the proceeds, if any, will be remitted for payment to the holders whose separate senior notes were remarketed in the remarketing. If a holder of senior notes elects to have its senior notes remarketed during any remarketing period but the remarketing agent fails to remarket the senior notes during such remarketing period, the senior notes will be promptly returned to the custodial agent for release to the holder at the end of that period.

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What is the settlement rate?

        The settlement rate is the number of newly issued Common Shares that Platinum Holdings is obligated to sell and you are obligated to purchase upon settlement of a purchase contract on the share purchase date.

        The settlement rate for each purchase contract, subject to adjustment under specified circumstances, will be as follows:

•

if the applicable market value, determined as described below, of the Common Shares is equal to or greater than $                                , the settlement rate will be            Common Shares per purchase contract;

•

if the applicable market value of the Common Shares is less than $                                but greater than $                                , the settlement rate will be equal to $25 divided by the applicable market value of the Common Shares per purchase contract; or

•

if the applicable market value of the Common Shares is less than or equal to $                                , the settlement rate will be             Common Shares per purchase contract.

        "Applicable market value" means the average of the closing price per Common Share on each of the 20 consecutive trading days ending on the third trading day immediately preceding the share purchase date.

        At the option of each holder, a purchase contract may be settled early by the early delivery of cash to the purchase contract agent, as described below, in which case the settlement rate will be            Common Shares per purchase contract.

Besides participating in a remarketing, how else can my obligations under the purchase contract be satisfied?

        Besides participating in the remarketing, your obligations under the purchase contract may also be satisfied:

•

if you have created stripped units or elected not to participate in the remarketing, by delivering and pledging specified treasury securities in substitution for your senior notes and applying the cash payments received upon maturity of those pledged treasury securities;

•

through the early delivery of cash to the purchase contract agent on or prior to the seventh business day prior to the share purchase date in the manner described in "Description of the Equity Security Units—Early Settlement";

•

by delivering cash on the business day prior to the share purchase date for settlement of the purchase contracts in the manner described in "Description of the Equity Security Units—Notice to Settle with Cash"; or

•

if Platinum Holdings is involved in a merger, acquisition or consolidation prior to the share purchase date in which at least 30% of the consideration for the Common Shares consists of cash or cash equivalents, through an early settlement of the purchase contract as described in "Description of the Equity Security Units—Early Settlement Upon Cash Merger."

        If a holder of a unit elects not to participate in a remarketing and does not give notice to the purchase contract agent that the holder intends to settle the purchase contract with cash on the share purchase date, Platinum Holdings will exercise its rights as a secured party in respect of the pledged securities to satisfy the holder's obligation to purchase Common Shares.

        In addition, the purchase contracts, Platinum Holdings' related rights and obligations and those of the holders of the units, including their rights to receive accumulated contract adjustment payments or deferred contract adjustment payments and obligations to purchase Common Shares,

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will automatically terminate upon the occurrence of Platinum Holdings' bankruptcy, insolvency or reorganization. Upon such a termination of the purchase contracts, the pledged senior notes or treasury securities will be released and distributed to you. If Platinum Holdings becomes the subject of a case under the federal bankruptcy code, a delay may occur as a result of the imposition of an automatic stay under the bankruptcy code and continue until the automatic stay has been lifted. The automatic stay will not be lifted until such time as the bankruptcy judge agrees to lift it and allows your collateral to be returned to you. Similarly, if Platinum Holdings becomes the subject of winding up proceedings under the Bermuda Companies Act 1981, a delay may result from the automatic stay of proceedings against Platinum Holdings and may continue until the court decides to lift the stay.

        If the purchase contract is settled early or is terminated as the result of Platinum Holdings' bankruptcy, insolvency or reorganization as described above, a holder will have no further right to receive any accrued contract adjustment payments or deferred contract adjustment payments.

Under what circumstances may Platinum Finance redeem the senior notes before they mature?

        If the tax laws change or are interpreted by the tax authorities or the courts in a way that adversely affects our tax consequences with respect to the senior notes, then Platinum Finance may elect to redeem the senior notes. If the senior notes are redeemed before a successful remarketing, the money received from the redemption will be used by the collateral agent to purchase a portfolio of zero-coupon U.S. treasury securities that mature on or prior to each payment date of the senior notes through the share purchase date, in an aggregate amount equal to the principal on the senior notes included in normal units and the interest that would have been due on such payment date on the senior notes included in normal units. For a holder of normal units, these treasury securities will replace the senior notes as the collateral securing such holder's obligations to purchase Common Shares under the purchase contracts. If your senior notes are not components of normal units, you, rather than the collateral agent, will receive the related redemption payment. If the senior notes are redeemed, then each unit will consist of a purchase contract for Common Shares and an ownership interest in the portfolio of treasury securities.

What is the maturity of the senior notes?

        The senior notes will mature on            , 2007.

What is the extent of Platinum Holdings' guarantee?

        Platinum Holdings will irrevocably guarantee the payment in full of the following:

•

interest payments that are required to be paid on the senior notes; and

•

the principal amount of the senior notes.

        The guarantee will be unsecured and rank equally in right of payment to all other senior unsecured debt of Platinum Holdings. Under "What payments will be made to holders of the units and the senior notes?" we explain the extent to which Platinum Holdings' obligations under the guarantee will be effectively junior to the debt and other obligations of its subsidiaries.

        The senior notes and the guarantee do not limit Platinum Holdings' or Platinum Finance's ability or the ability of their respective subsidiaries to incur indebtedness. This would include indebtedness that ranks equally with the senior notes and the guarantee.

What are the U.S. federal income tax consequences related to the units and senior notes?

        If you purchase units in the ESU Offering, you will be treated for U.S. federal income tax purposes as having acquired purchase contracts and ownership interests in the senior notes

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constituting those units, and by purchasing the units you agree to treat the purchase contracts and ownership interests in the senior notes in that manner for all tax purposes. In addition, you agree to treat the senior notes as indebtedness of Platinum Finance for all tax purposes. You must allocate the purchase price of the units between purchase contracts and ownership interests in the senior notes in proportion to their respective fair market values, which will establish your initial tax basis in each component of the units. Platinum Holdings and Platinum Finance expect to report the fair market value of each purchase contract as $0.00 and the fair market value of each senior note as $1,000 (or $25 for each 2.5% ownership interest in a senior note included in a normal unit).

        For U.S. federal income tax purposes, we intend to treat the senior notes as contingent payment debt instruments subject to the "noncontingent bond method" of accruing original issue discount. As discussed more fully under "U.S. Federal Income Tax Consequences—Senior Notes—Original Issue Discount", the effects of this method will be (1) to require you, regardless of your usual method of tax accounting, to use an accrual method with respect to interest on the senior notes, (2) to require you, for all accrual periods through             , 2005, and possibly thereafter, to accrue interest income in excess of distributions actually received by you, and (3) generally to result in ordinary rather than capital treatment of any gain or loss on the sale, exchange or disposition of an ownership interest in the senior notes or the units to the extent attributable to the senior notes.

        Because there is no statutory, judicial or administrative authority directly addressing the tax treatment of units or instruments similar to units, you are urged to consult your own tax advisor concerning the tax consequences of an investment in units. For additional information, see "U.S. Federal Income Tax Consequences."

What are the ERISA considerations?

        Plans subject to Title I of the U.S. Employee Retirement Income Security Act of 1974 ("ERISA") or Section 4975 of the Internal Revenue Code of 1986, as amended, may invest in the equity units subject to the considerations set forth in "ERISA Considerations."

Will the units be listed on a stock exchange?

        The normal units have been approved for listing, subject to notice of issuance, on the New York Stock Exchange under the symbol "PTP Pr M". We have no obligation and do not currently intend to apply for any separate listing of either the stripped units or the senior notes on any stock exchange.

What are the expected uses of proceeds from the offerings?

        We estimate that Platinum Finance will receive net proceeds from the ESU Offering of approximately $120 million, or $138 million if the underwriters' option to purchase additional units is exercised in full. We anticipate that Platinum Finance will retain $20 million of the net proceeds, or $23 million if the underwriters exercise their option to purchase additional equity security units in full, and contribute the rest to Platinum US, its wholly owned subsidiary. Platinum Finance intends to use the retained portion of the net proceeds of the offering to fund the interest payments on the senior notes payable on or prior to the share purchase date.

        Assuming the Common Shares are offered at an initial public offering price of $22.50 per Common Share (the midpoint of the range at which Platinum Holdings proposes to offer the Common Shares), the net proceeds from the Equity Public Offering are estimated to be between approximately $640 million (assuming no exercise of the underwriters' option to purchase additional Common Shares) and $736 million (assuming full exercise of the underwriters' option to purchase additional Common Shares). A portion of the net proceeds of the Equity Public Offering, the RenaissanceRe Investment and the Cash Contribution, currently estimated at approximately $10 million, will be retained by Platinum Holdings and the balance will be contributed to the capital of Platinum US (in an amount not less than $250 million, including the contribution of net proceeds of the ESU Offering described above), Platinum UK (in an amount not less than $150 million, upon its being licensed in the United Kingdom), Platinum Ireland (in an amount not less than $100 million, substantially all of which will be used to purchase a surplus note issued by Platinum US) and Platinum Bermuda (in an amount not less than $375 million).

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The ESU Offering—Explanatory Diagrams

        The following diagrams demonstrate some of the key features of the purchase contracts, normal units, stripped units and senior notes, and the transformation of normal units into stripped units and senior notes. The following diagrams assume that the senior notes are successfully remarketed, the interest rate on the senior notes is reset, there is no early settlement and the payment of contract adjustment payments is not deferred.

Purchase Contracts

•

Normal units and stripped units both include a purchase contract under which you agree to purchase Common Shares on the share purchase date.

•

The number of Common Shares to be purchased under each purchase contract will depend on the "applicable market value." The "applicable market value" means the average of the closing price per Common Share on each of the 20 consecutive trading days ending on the third trading day immediately preceding the share purchase date.

(1)

The "reference price" is $                        , which is the initial public offering price of the Common Shares.

(2)

The "threshold appreciation price" is $                                , which is            % of the reference price.

(3)

For each of the percentage categories shown, the percentage of the Common Shares to be delivered on the share purchase date to a holder of normal units or stripped units is determined by dividing

•

the related number of Common Shares to be delivered, as indicated in the footnote for each such category, by

•

an amount equal to $25, the stated amount of the unit, divided by the reference price.

(4)

If the applicable market value of the Common Shares is less than or equal to the reference price, the number of Common Shares to be delivered will be calculated by dividing the stated amount of $25 by the reference price.

(5)

If the applicable market value of the Common Shares is between the reference price and the threshold appreciation price, the number of Common Shares to be delivered will be calculated by dividing the stated amount of $25 by the applicable market value.

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(6)

If the applicable market value of the Common Shares is greater than or equal to the threshold appreciation price, the number of Common Shares to be delivered will be calculated by dividing the stated amount of $25 by the threshold appreciation price.

Normal Units

•

A normal unit will consist of two components as illustrated below:





•

After a successful remarketing or tax event redemption, the normal units will include specified treasury securities in lieu of the senior notes.





•

If you hold a normal unit, you will hold an ownership interest in a senior note and, after a successful remarketing or tax event redemption, an ownership interest in specified treasury securities, but will pledge that interest to the collateral agent for the benefit of Platinum Holdings to secure your obligations under the purchase contract.





•

If you hold a normal unit, you may also substitute a specified amount of treasury securities for the ownership interest in a senior note if you decide not to participate in the remarketing.

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Stripped Units

•

A stripped unit consists of two components as illustrated below:





•

If you hold a stripped unit, you own a 1/40, or 2.5%, interest in the treasury security but will pledge it to the collateral agent for the benefit of Platinum Holdings to secure your obligations under the purchase contract. The treasury security is a zero-coupon U.S. treasury security (CUSIP No.            ) that matures on             , 2005.

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Senior Notes

•

Senior notes will have the terms illustrated below:

•

If you hold an ownership interest in a senior note that is a component of a normal unit, you have the option to either:



•

allow the ownership interest in the senior note to be included in the remarketing process, the proceeds of which will be used to purchase treasury securities, if the remarketing is successful, which will be applied to settle the purchase contract; or



•

elect not to participate in the remarketing by delivering treasury securities in substitution for the ownership interest in the senior note, the proceeds of which will be applied to settle the related purchase contract.




•

If you hold a senior note that is not a component of a normal unit, you have the option to either:



•

continue to hold the senior note the rate of which will be reset, effective from the settlement date of a successful remarketing of the senior notes; or



•

deliver the senior note to the remarketing agent to be included in the remarketing.

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Transforming Normal Units into Stripped Units and Senior Notes

•

To create stripped units, you must substitute for the pledged ownership interest in the senior note (or, after a successful remarketing or tax event redemption, the pledged treasury securities) the specified zero-coupon U.S. treasury security that matures on            , 2005.



•

The pledged senior note or the pledged treasury securities will be released from the pledge and delivered to you.



•

The zero-coupon U.S. treasury security together with the purchase contract would then constitute a stripped unit. The senior note (or, after a successful remarketing, treasury securities), which was previously a component of normal units, is tradable as a separate security.



•

The transformation of normal units into stripped units and senior notes and the transformation of stripped units and senior notes into normal units may generally be effected only in integral multiples of 40 units, as more fully described in this prospectus. If, however, the senior notes constituting a part of the normal units have been replaced with treasury securities due to a successful remarketing or tax event redemption, the transformation of normal units into stripped units and the recreation of normal units from stripped units may be effected only in integral multiples of units such that both the treasury securities to be deposited and the treasury securities to be released are in integral multiples of $1,000, as more fully described in this prospectus.

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        The following illustration depicts the transformation of 40 normal units into 40 stripped units and one $1,000 principal amount senior note.

•

After remarketing, the normal units will include ownership interests in specified U.S. treasury securities in lieu of an ownership interest in senior notes.



•

You can also transform stripped units and senior notes (or, after a successful remarketing or tax event redemption, treasury securities) into normal units. Following that transformation, the specified zero-coupon U.S. treasury security, which was previously a component of the stripped units, is tradable as a separate security.

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Selected Pro Forma Financial Information and Operating Data

        Financial information in this prospectus is presented in U.S. dollars and on the basis of U.S. GAAP unless otherwise indicated.

        In this prospectus, we are presenting unaudited pro forma financial information of Platinum Holdings with respect to the Transferred Business, contingent upon the completion of the Equity Public Offering. This pro forma financial information is based on the terms of the agreements between Platinum and St. Paul effecting the transfer of the Transferred Business, the material terms of which are described under "Certain Relationships and Related Transactions", which we refer to herein as the "Inception Agreements."

        We caution that the Platinum pro forma consolidated balance sheet and pro forma combined underwriting results presented herein are not indicative of the actual results that we expect to achieve once we commence operations. Many factors may cause our actual results to differ materially from the pro forma consolidated balance sheet and underwriting results including, but not limited to, the following:

•

Platinum's pro forma combined statement of underwriting results includes premium and loss development on business entered into prior to January 1, 2002. Under the Quota Share Retrocession Agreements, we are assuming no premium or loss development on business entered into prior to January 1, 2002. Therefore, our reported premiums written and earned and reported losses and loss adjustment expenses, which are the expenses of settling claims, in our initial years of operation could be substantially lower than as presented in Platinum's pro forma combined statement of underwriting results. As such, our reported results in our initial years of operation will not be subject to prior year development for periods prior to January 1, 2002.



•

Following the Equity Public Offering, we will report underwriting results under the Quota Share Retrocession Agreements for the period through the date of completion of the Equity Public Offering based on the application of retroactive reinsurance accounting, resulting in the premiums earned and losses incurred by St. Paul during such period being excluded from our statement of underwriting results. Due to this exclusion, following the Equity Public Offering, our reported 2002 premiums written and earned and our net underwriting results in 2002 could be substantially different than as presented in Platinum's pro forma combined statement of underwriting results.



•

Platinum's pro forma consolidated balance sheet reflects the inception of the Quota Share Retrocession Agreements assuming transferred balances as of June 30, 2002. Platinum's actual consolidated balance sheet will report transferred amounts determined as of 12:01 a.m. on the day immediately following the date of completion of the Equity Public Offering. Accordingly, underwriting gain or loss with respect to the Assumed Reinsurance Contracts for the period from January 1, 2002 through such date will be retained by St. Paul.



•

Although we expect to continue to be afforded the benefits of most of St. Paul Re's retrocessional reinsurance program through their expiration during 2002, we may enter into retrocessional reinsurance contracts with significantly different terms and conditions from those that have been made available to us from St. Paul Re and which form the basis of our initial operations.



•

The additional and reinstatement premiums, which are premiums charged for the restoration of the limit of a catastrophe contract to its full amount after payment of losses, recorded in 2001 by St. Paul Re's Finite Risk operating segment were primarily caused by losses relating to the September 11, 2001 terrorist attack. These additional and reinstatement premiums

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were unusually high and not necessarily indicative of the recurring premium volume we expect to write in that business segment.

•

Platinum's pro forma financial statements continue to reflect the discounting of the liability for certain Assumed Reinsurance Contracts based on our current intention to make arrangements to permit such discounting. If we do not put such arrangements in place, reinsurance contracts of a similar type entered into in the future would be reported on an undiscounted basis.

Pro Forma Consolidated Balance Sheet Data

        We have prepared our unaudited pro forma consolidated balance sheet as of June 30, 2002 to reflect our initial capitalization in the amount of $120,000 and adjusted to reflect, among other things,

•

amounts reflecting (a) the receipt of approximately $725 million, representing the estimated net proceeds from the Equity Public Offering and the RenaissanceRe Investment based on an assumed initial public offering price of $22.50 per Common Share (the midpoint of the range at which Platinum Holdings proposes to offer the Common Shares), without giving effect to any exercise of the underwiters', St. Paul's or RenaissanceRe's options to purchase additional Common Shares in connection with the Equity Public Offering, (b) the redemption of the Common Shares that were issued at inception and capital contributed prior to the Equity Public Offering, (c) the payment of certain formation and organization expenses, as discussed in Note 2 and Note 12 on pages F-5 and F-13 of this prospectus, which total $5.1 million, of which $2.1 million has been expensed as of June 30, 2002, and (d) our entering into, and accruing for, the Services and Capacity Reservation Agreement as of June 30, 2002