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                                                                     EXHIBIT 1.1


                                1,200,000 SHARES



                      WHITE MOUNTAINS INSURANCE GROUP, LTD.

                    COMMON SHARES, PAR VALUE $1.00 PER SHARE



                             UNDERWRITING AGREEMENT

__________, 2002
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                                                             _____________, 2002

Morgan Stanley & Co. Incorporated
Banc of America Securities LLC
Credit Suisse First Boston Corporation
Lehman Brothers Inc.
Merrill Lynch, Pierce, Fenner & Smith Incorporated
  as representatives of the Underwriters
c/o  Morgan Stanley & Co. Incorporated
     1585 Broadway
     New York, New York 10036

Dear Sirs and Mesdames:

         White Mountains Insurance Group, Ltd., a Bermuda corporation (the
"COMPANY"), proposes to issue and sell to the several Underwriters named in
Schedule II hereto (the "UNDERWRITERS"), and a shareholder of the Company (the
"SELLING SHAREHOLDER") named in Schedule I hereto severally propose to sell to
the several Underwriters, an aggregate of 1,200,000 shares of the Common Shares
($1.00 par value per share) of the Company (the "FIRM SHARES"), of which
1,000,000 shares are to be issued and sold by the Company and 200,000 shares are
to be sold by the Selling Shareholder.

         The Company also proposes to issue and sell to the several Underwriters
not more than an additional 150,000 shares of its Common Shares (the "ADDITIONAL
SHARES") if and to the extent that you, as Managers of the offering, shall have
determined to exercise, on behalf of the Underwriters, the right to purchase
such shares of common stock granted to the Underwriters in Section 3 hereof. The
Firm Shares and the Additional Shares are hereinafter collectively referred to
as the "SHARES." The Common Shares of the Company to be outstanding after giving
effect to the sales contemplated hereby are hereinafter referred to as the
"COMMON STOCK." The Company and the Selling Shareholder are hereinafter
sometimes collectively referred to as the "SELLERS."

         In connection with the sale of Shares by the Selling Shareholder, the
Company and the Selling Shareholder have entered into a custody agreement dated
[ ], 2002 (the "CUSTODY AGREEMENT").

         The Company has filed with the Securities and Exchange Commission (the
"COMMISSION") a registration statement on Form S-3 (File No. 333-88352),
including a prospectus, relating to the Shares. The registration statement as
amended at the time it becomes effective, including the information (if any)
deemed to be part of the registration statement at the time of effectiveness
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pursuant to Rule 430A under the Securities Act of 1933, as amended (the
"SECURITIES ACT"), is hereinafter referred to as the "REGISTRATION STATEMENT";
the prospectus in the form first used to confirm sales of Shares is hereinafter
referred to as the "PROSPECTUS." If the Company has filed an abbreviated
registration statement to register additional shares of Common Stock pursuant to
Rule 462(b) under the Securities Act (the "RULE 462 REGISTRATION STATEMENT"),
then any reference herein to the term "REGISTRATION STATEMENT" shall be deemed
to include such Rule 462 Registration Statement.

         1. REPRESENTATIONS AND WARRANTIES OF THE COMPANY. The Company
represents and warrants to and agrees with each of the Underwriters that:

                  (a) The Company and the transactions contemplated by this
         Agreement meet the requirements for the use of Form S-3 under the
         Securities Act. The Registration Statement has become effective; no
         stop order suspending the effectiveness of the Registration Statement
         is in effect, and no proceedings for such purpose are pending before or
         threatened by the Commission.

                  (b) (i) The Registration Statement, when it became effective,
         did not contain and, as amended or supplemented, if applicable, will
         not contain any untrue statement of a material fact or omit to state a
         material fact required to be stated therein or necessary to make the
         statements therein not misleading, (ii) the Registration Statement and
         the Prospectus comply and, as amended or supplemented, if applicable,
         will comply in all material respects with the Securities Act and the
         applicable rules and regulations of the Commission thereunder and (iii)
         the Prospectus does not contain and, as amended or supplemented, if
         applicable, will not contain any untrue statement of a material fact or
         omit to state a material fact necessary to make the statements therein,
         in the light of the circumstances under which they were made, not
         misleading, except that the representations and warranties set forth in
         this paragraph do not apply to statements or omissions in the
         Registration Statement or the Prospectus based upon information
         relating to any Underwriter furnished to the Company in writing by such
         Underwriter through you expressly for use therein. Each document filed
         or to be filed pursuant to the Exchange Act and incorporated by
         reference in the Prospectus, when read in conjunction with all such
         documents, did not contain or will not contain when so filed any untrue
         statement of a material fact or omit to state a material fact required
         to be stated therein or necessary to make the statements therein not
         misleading, and complied or will comply when so filed in all material
         respects with the Exchange Act and the rules and regulations of the
         Commission thereunder. No order preventing or suspending the use of any
         preliminary prospectus has been issued by the Commission and no
         proceedings for that purpose shall have been instituted or, to the


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         knowledge of the Company, threatened or contemplated by the Commission.

                  (c) PricewaterhouseCoopers LLP, whose reports are included or
         incorporated by reference in the Prospectus, are independent certified
         public accountants with respect to the Company and its subsidiaries and
         CGU Corporation and its subsidiaries within the meaning of the
         Securities Act and the rules and regulations adopted by the Commission
         thereunder. The financial statements of the Company and its
         subsidiaries and CGU Corporation and its subsidiaries (including the
         related notes and supporting schedules) included or incorporated by
         reference in the Prospectus present fairly in all material respects the
         financial condition, results of operations and cash flows of the
         entities purported to be shown thereby at the dates and for the periods
         indicated and have been prepared in accordance with generally accepted
         accounting principles applied on a consistent basis throughout the
         periods indicated and conform in all material respects with the rules
         and regulations adopted by the Commission under the Securities Act,
         except as otherwise noted therein; and the supporting schedules
         included or incorporated by reference in the Prospectus present fairly
         in all material respects the information required to be stated therein.
         The PRO FORMA consolidated financial information included or
         incorporated by reference in the Prospectus (i) is presented fairly in
         all material respects, (ii) has been prepared in accordance with the
         rules and regulations under the Securities Act with respect to PRO
         FORMA statements and (iii) has been properly compiled on the bases
         described therein, and the assumptions used in the preparation of the
         PRO FORMA consolidated financial information included or incorporated
         by reference in the Prospectus are reasonable and the adjustments used
         therein are appropriate to give effect to the transactions or
         circumstances referred to therein. The foregoing representations in
         this paragraph 1(c) regarding the fair presentation provided by (x) the
         financial statements of CGU Corporation and its subsidiaries and (y)
         the PRO FORMA consolidated financial information are qualified in their
         entirety to the extent that the information contained in such
         statements may be affected by the subsequent write-off of assets or the
         establishment or increase in liabilities and related adjustments
         (collectively, "adjustments") PROVIDED that such subsequent adjustments
         and their effects on such statements are fairly disclosed in all
         material respects in the Prospectus.

                  (d) Each of the Company and each of the subsidiaries of the
         Company listed on Schedule III hereto (the "Designated Subsidiaries")
         has been duly organized or formed and is validly existing in good
         standing (including, in the case of the Company, as an exempted
         company) under the laws of the jurisdiction of its organization or
         formation, with full power and authority to own, lease and operate its
         properties and conduct


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         its business as described in the Prospectus and to enter into and
         perform its obligations under this Agreement and the Custody Agreement;
         and each of the Company and the Designated Subsidiaries is duly
         qualified to do business as described in the Prospectus and is in good
         standing in each jurisdiction in which the character of the business
         conducted by it or the location of the properties owned, leased or
         operated by it make such qualification necessary, except where the
         failure to so qualify would not, individually or in the aggregate, have
         a material adverse effect on the condition (financial or otherwise),
         results of operations, business or prospects of the Company and its
         subsidiaries taken as a whole (a "MATERIAL ADVERSE EFFECT"). The
         Designated Subsidiaries, on an unconsolidated basis, for the
         three-month period ended on March 31, 2002 accounted for in the
         aggregate at least 90% of the premiums earned by the Company and its
         consolidated subsidiaries in each of its property and casualty business
         (exclusive of the reinsurance business) and its reinsurance business.

                  (e) The capitalization of the Company as of March 31, 2002 is
         as set forth in the Prospectus. All of the outstanding shares of
         capital stock of the Company and each Designated Subsidiary of the
         Company that is a corporation have been duly authorized and validly
         issued and are fully paid and nonassessable. Except as disclosed in the
         Prospectus, all of the outstanding shares of capital stock, partnership
         interests or other ownership interests of each Designated Subsidiary of
         the Company are owned directly or indirectly by the Company free and
         clear of any claim, lien, encumbrance, security interest, restriction
         upon voting or transfer, preemptive rights or any other claim of any
         third party.

                  (f) Except as described in or contemplated by the Registration
         Statement and the Prospectus (exclusive of any amendments or
         supplements thereto subsequent to the date of this Agreement), (i)
         there has not been any event or development that has had or would
         reasonably be expected to have, individually or in the aggregate, a
         Material Adverse Effect, from the respective dates as of which
         information is given in the Prospectus and (ii) since such dates, there
         has not been any material increase in the long-term debt or, to the
         knowledge of the Company after due inquiry, in the loss and loss
         adjustment expense reserves (net of applicable reinsurance
         recoverables) of the Company and its consolidated subsidiaries.

                  (g) None of (i) the execution or delivery hereof or of the
         Custody Agreement by the Company, (ii) the consummation of the
         transactions contemplated hereby or thereby, (iii) the issuance and
         delivery of the Shares by the Company or (iv) compliance by the Company
         with all of the provisions of this Agreement or of the Custody


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         Agreement, (A) will result in a breach or violation of, or constitute a
         default under, the certificate of incorporation, by-laws, partnership
         agreement or other governing documents of the Company or any of the
         Designated Subsidiaries, (B) will result in a breach or violation of,
         or constitute a default under, any agreement, indenture or other
         instrument to which the Company or any of the Designated Subsidiaries
         is a party or by which any of them is bound, or to which any of their
         properties is subject, (C) will result in a violation of any law, rule,
         administrative regulation or decree of any court, or any governmental
         agency or body having jurisdiction over the Company, the Designated
         Subsidiaries or any of their respective properties, or (D) will result
         in the creation or imposition of any lien, charge, claim or encumbrance
         upon any property or asset of the Company, or any Designated Subsidiary
         except (other than with respect to clause (A) above) as would not have,
         individually or in the aggregate, a Material Adverse Effect. Except for
         permits, consents, approvals and similar authorizations required under
         the securities or "Blue Sky" laws of certain jurisdictions, and except
         for such permits, consents, approvals and authorizations which have
         been obtained, no permit, consent, approval, authorization or order of
         any court, governmental agency or body or financial institution is
         required in connection with the consummation of the transactions
         contemplated by this Agreement or the Custody Agreement.

                  (h) This Agreement and the Custody Agreement have been duly
         authorized, executed and delivered by the Company.

                  (i) None of the Company or any of its Designated Subsidiaries
         (i) is in violation of its certificate of incorporation or by-laws or
         other governing documents, (ii) is in default and no event has occurred
         which, with notice or lapse of time or both, would constitute such a
         default, in the due performance or observance of any term, covenant or
         condition contained in any agreement, indenture or other instrument to
         which it is a party or by which it is bound or to which any of its
         properties is subject, except for any such defaults that would not,
         individually or in the aggregate, have a Material Adverse Effect, or
         (iii) is in violation of any insurance law or insurance regulation to
         which it or its property may be subject, except for any such violations
         that would not, individually or in the aggregate, have a Material
         Adverse Effect.

                  (j) The Company is able to pay its liabilities as they become
         due.

                  (k) The Shares to be sold by the Company have been duly and
         validly authorized by the Company for issuance and sale to the
         Underwriters pursuant to this Agreement and, when issued and delivered


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         in accordance with the terms of this Agreement, will be validly issued,
         fully paid and non-assessable, and the issuance of such Shares will not
         be subject to any preemptive or similar rights. The authorized capital
         stock of the Company conforms in all material respects to the
         description thereof in the Registration Statement and the Prospectus.
         Neither the filing of the Registration Statement nor the offering or
         sale of the Shares as contemplated by this Agreement gives rise to any
         rights, other than those which have been duly waived or satisfied, for
         or relating to the registration of any securities of the Company.

                  (l) The shares of Common Stock (including the Shares to be
         sold by the Selling Shareholder) outstanding prior to the issuance of
         the Shares to be sold by the Company have been duly authorized and are
         validly issued, fully paid and non-assessable.

                  (m) There are no contracts or other documents which are
         required to be described in the Prospectus or filed as exhibits to the
         Registration Statement or the documents incorporated by reference
         therein by the Securities Act or the Exchange Act, as the case may be,
         which have not been described in the Prospectus or filed as exhibits to
         the Registration Statement or the documents incorporated by reference
         therein as permitted by the Securities Act or Exchange Act, as the case
         may be.

                  (n) There is no litigation or governmental proceeding to which
         the Company or any of its subsidiaries is a party or to which any
         property of the Company or any of its subsidiaries is subject or which
         is pending or, to the knowledge of the Company, threatened against the
         Company or any of its subsidiaries that could reasonably be expected
         to, individually or in the aggregate, result in a Material Adverse
         Effect, or which is required to be disclosed in the Prospectus or to be
         filed as an exhibit to the Registration Statement and is not disclosed
         or filed as required.

                  (o) Each of the Company and its subsidiaries has (i) all
         licenses, certificates, permits, authorizations, approvals, franchises
         and other rights from, and has made all declarations and filings with,
         all federal, state and local governmental authorities (including,
         without limitation, from the insurance regulatory agencies of the
         various jurisdictions where it conducts business) and all courts and
         other governmental tribunals (each, an "Authorization") necessary to
         engage in the business currently conducted by it in the manner
         described in the Prospectus, except where failure to hold such
         Authorizations would not reasonably be expected to have, individually
         or in the aggregate, a Material Adverse Effect, (ii) fulfilled and
         performed all obligations necessary to maintain each Authorization,
         except where the failure to fulfill or perform an obligation or to
         maintain an Authorization and would


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         not reasonably be expected to have, individually or in the aggregate, a
         Material Adverse Effect, (iii) no knowledge of any threatened action,
         suit, proceeding or investigation that would reasonably be expected to
         result in the revocation, termination or suspension of any
         Authorization, the revocation, termination or suspension of which would
         reasonably be expected to have a Material Adverse Effect. Except as
         would not reasonably be expected to have, individually or in the
         aggregate, a Material Adverse Effect, all such Authorizations are valid
         and in full force and effect and the Company and its subsidiaries are
         in compliance in all material respects with the terms and conditions of
         all such Authorizations and with the rules and regulations of the
         regulatory authorities having jurisdiction with respect thereto. No
         insurance regulatory agency or body has issued any order or decree
         impairing, restricting or prohibiting the payment of dividends by any
         subsidiary of the Company to its parent, other than any such orders or
         decrees the issuance of which could not reasonably be expected to have,
         individually or in the aggregate, a Material Adverse Effect.

                  (p) The 2001 statutory annual statements of each Designated
         Subsidiary which is a regulated insurance subsidiary of the Company and
         the statutory balance sheets and income statements included in such
         statutory annual statements together with related schedules and notes,
         have been prepared, in all material respects, in conformity with
         statutory accounting principles or practices required or permitted by
         the appropriate insurance regulator of the jurisdiction of domicile of
         each such subsidiary, and such statutory accounting practices have been
         applied on a consistent basis throughout the periods involved, except
         as may otherwise be indicated therein or in the notes thereto, and
         present fairly, in all material respects, the statutory financial
         position of such insurance subsidiaries as of the dates thereof, and
         the statutory basis results of operations of such insurance
         subsidiaries for the periods covered thereby PROVIDED, HOWEVER, that
         the Company makes no - representations or warranties as to the
         financial information, financial statements and other related documents
         that were the responsibility of, and prepared by the former management
         of, and for the benefit of CGU Corporation.

                  (q) The Company and its insurance subsidiaries have made no
         material changes in their insurance reserving practices since
         December 31, 2001, except where such change in such insurance
         reserving practices would not reasonably be expected to have a
         Material Adverse Effect.

                  (r) The Company is not aware of any threatened or pending
         downgrading of any Designated Subsidiary's claims-paying ability rating
         or in the rating accorded any of the Company's securities by A.M. Best
         Company, Inc. or any other "naturally recognized statistical rating


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         organization" as such term is defined for purposes of Rule 436(g)(2)
         under the Securities Act.

                  (s) Each preliminary prospectus filed as part of the
         registration statement as originally filed or as part of any amendment
         thereto, or filed pursuant to Rule 424 under the Securities Act,
         complied when so filed in all material respects with the Securities Act
         and the applicable rules and regulations of the Commission thereunder.

                  (t) The Company is not, and after giving effect to the
         offering and sale of the Shares and the application of the proceeds
         thereof as described in the Prospectus will not be, required to
         register as an "investment company" as such term is defined in the
         Investment Company Act of 1940, as amended.

                  (u) The Company believes that it is not (i) a "passive foreign
         investment company," (ii) a "controlled foreign corporation," (iii) a
         "personal holding company," (iv) a "foreign personal holding company,"
         or (v) a "foreign investment company," all within the meaning of the
         Internal Revenue Code of 1986, as amended (the "Code"). In addition,
         the Company believes that none of its premium income, or that of any of
         its foreign subsidiaries, will be taxed as "related person insurance
         income" within the meaning of the Code.

                  (v) None of the Underwriters or any subsequent purchasers of
         the Shares (other than purchasers resident in Bermuda for Bermuda
         exchange control purposes) is subject to any stamp duty, excise or
         similar tax imposed in Bermuda in connection with the offering, sale or
         purchase of the Shares.

                  (w) There are no currency exchange control laws or withholding
         taxes of Bermuda that would be applicable to the payment of dividends
         on the Shares by the Company.

                  (x) Consummation of the transactions contemplated by this
         Agreement, including but not limited to any actions taken pursuant to
         the indemnification and contribution provisions set forth herein, will
         not constitute unlawful financial assistance under Bermuda law.

         2. REPRESENTATIONS AND WARRANTIES OF THE SELLING SHAREHOLDER. The
Selling Shareholder represents and warrants to and agrees with each of the
Underwriters that:

                  (a) This Agreement has been duly authorized, executed and
         delivered by or on behalf of the Selling Shareholder.


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                  (b) The execution and delivery by the Selling Shareholder of,
         and the performance by the Selling Shareholder of its obligations
         under, this Agreement, the Custody Agreement and the [Power of
         Attorney] appointing certain individuals as the Selling Shareholder's
         attorneys-in-fact to the extent set forth therein, relating to the
         transactions contemplated hereby and by the Registration Statement
         [(the "POWER OF ATTORNEY")] will not contravene (i) the certificate of
         incorporation or by-laws of the Selling Shareholder or (ii) any
         agreement or other instrument binding upon the Selling Shareholder or
         any applicable law, judgment, order or decree of any governmental body,
         agency or court having jurisdiction over the Selling Shareholder,
         except for the contravention of an agreement, instrument or applicable
         law which would not materially and adversely affect the consummation of
         the transactions contemplated by this Agreement by the Selling
         Shareholder, and no consent, approval, authorization or order of, or
         qualification with, any governmental body or agency is required for the
         performance by the Selling Shareholder of its obligations under this
         Agreement or the Custody Agreement or [Power of Attorney] of the
         Selling Shareholder, except such as may be required by the securities
         or Blue Sky laws of the various states in connection with the offer and
         sale of the Shares and except for any filing or disclosure that may be
         required of the Selling Shareholder under Canadian securities laws or
         the rules of the Toronto Stock Exchange, PROVIDED that any failure to
         make such a filing or disclosure would not materially and adversely
         affect the transactions contemplated by this Agreement.

                  (c) The Custody Agreement and the [Power of Attorney] have
         been duly authorized, executed and delivered by the Selling Shareholder
         and are valid and binding agreements of the Selling Shareholder except
         as the enforcement thereof may be limited by bankruptcy, insolvency,
         reorganization, moratorium or other similar laws relating to or
         affecting the rights and remedies of creditors or by general equitable
         principles.

                  (d) The Selling Shareholder has, and on the Closing Date will
         have, valid title to, or a valid "security entitlement" within the
         meaning of Section 8-102 of the New York Uniform Commercial Code
         ("UCC") in respect of, the Shares to be sold by the Selling Shareholder
         free and clear of all security interests, claims, liens, equities or
         other encumbrances and the legal right and power, and all authorization
         and approval required by law, to enter into this Agreement, the Custody
         Agreement and the [Power of Attorney] and to sell, transfer and deliver
         the Shares to be sold by the Selling Shareholder or a security
         entitlement in respect of such Shares.

                  (e) Upon payment for the Shares to be sold by the Selling
         Shareholder pursuant to this Agreement, delivery of such Shares, as


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         directed by the Underwriters, to Cede & Co. ("CEDE") or such other
         nominee as may be designated by the Depository Trust Company ("DTC"),
         registration of such Shares in the name of Cede or such other nominee
         and the crediting of such Shares on the records of DTC to securities
         accounts of the Underwriters (assuming that neither DTC nor any such
         Underwriter has notice of any adverse claim to such Shares or any
         security entitlement in respect of such Shares), (A) DTC shall be a
         "protected purchaser" of such Shares within the meaning of Section
         8-303 of the UCC and (B) the Underwriters will acquire a security
         entitlement in respect of such Shares free and clear of any adverse
         claim.

                  (f) The Selling Shareholder is not prompted by any information
         concerning the Company or its subsidiaries which is not set forth in
         the Prospectus to sell its Shares pursuant to this Agreement.

                  (g) (i) The Registration Statement, when it became effective,
         did not contain and, as amended or supplemented, if applicable, will
         not contain any untrue statement of a material fact or omit to state a
         material fact required to be stated therein or necessary to make the
         statements therein not misleading and the Prospectus does not contain
         and, as amended or supplemented, if applicable, will not contain any
         untrue statement of a material fact or omit to state a material fact
         necessary to make the statements therein, in the light of the
         circumstances under which they were made, not misleading; PROVIDED that
         the representations and warranties set forth in this paragraph are
         limited to statements or omissions made in reliance upon information
         relating to the Selling Shareholder furnished to the Company in writing
         by the Selling Shareholder expressly for use in the Registration
         Statement, the Prospectus or any amendments or supplements thereto. It
         is understood and agreed that the only written information furnished to
         the Company by the Selling Shareholder specifically for use in the
         Registration Statement is the information relating to the Selling
         Shareholder set forth in the table under the caption "Principal and
         Selling Shareholders" in the Prospectus.

                  (h) The Selling Shareholder has not taken, and will not take,
         directly or indirectly, any action designed to, or which might
         reasonably be expected to, cause or result in stabilization or
         manipulation of the price of any security of the Company to facilitate
         the sale or resale of the Shares pursuant to the distribution
         contemplated by this Agreement, and the Selling Shareholder has not
         distributed and will not distribute any prospectus or other offering
         material in connection with the offering and sale of the Shares.

         3. AGREEMENTS TO SELL AND PURCHASE. Each Seller, severally and not
jointly, hereby agrees to sell to the several Underwriters, and each
Underwriter, upon the basis of the representations and warranties herein
contained, but subject


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to the conditions hereinafter stated, agrees, severally and not jointly, to
purchase from such Seller at $______ a share (the "PURCHASE PRICE") the number
of Firm Shares (subject to such adjustments to eliminate fractional shares as
you may determine) that bears the same proportion to the number of Firm Shares
to be sold by such Seller as the number of Firm Shares set forth in Schedule II
hereto opposite the name of such Underwriter bears to the total number of Firm
Shares.

         On the basis of the representations and warranties contained in this
Agreement, and subject to its terms and conditions, the Company agrees to sell
to the Underwriters the Additional Shares, and the Underwriters shall have the
right to purchase, severally and not jointly, up to 150,000 Additional Shares at
the Purchase Price. You may exercise this right on behalf of the Underwriters in
whole or from time to time in part by giving written notice of each election to
exercise the option not later than 30 days after the date of this Agreement. Any
exercise notice shall specify the number of Additional Shares to be purchased by
the Underwriters and the date on which such shares are to be purchased. Each
purchase date must be at least one business day after the written notice is
given and may not be earlier than the closing date for the Firm Shares nor later
than ten business days after the date of such notice. Additional Shares may be
purchased as provided in Section 5 hereof solely for the purpose of covering
over-allotments made in connection with the offering of the Firm Shares. On each
day, if any, that Additional Shares are to be purchased (an "OPTION CLOSING
DATE"), each Underwriter agrees, severally and not jointly, to purchase the
number of Additional Shares (subject to such adjustments to eliminate fractional
shares as you may determine) that bears the same proportion to the total number
of Additional Shares to be purchased on such Option Closing Date as the number
of Firm Shares set forth in Schedule II hereto opposite the name of such
Underwriter bears to the total number of Firm Shares.

         Each Seller hereby agrees that, without the prior written consent of
Morgan Stanley & Co. Incorporated on behalf of the Underwriters, it will not,
during the period ending 90 days after the date of the Prospectus, (i) offer,
pledge, sell, contract to sell, sell any option or contract to purchase,
purchase any option or contract to sell, grant any option, right or warrant to
purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any
shares of Common Stock or any securities convertible into or exercisable or
exchangeable for Common Stock or (ii) enter into any swap or other arrangement
that transfers to another, in whole or in part, any of the economic consequences
of ownership of the Common Stock, whether any such transaction described in
clause (i) or (ii) above is to be settled by delivery of Common Stock or such
other securities, in cash or otherwise.

         The restrictions contained in the preceding paragraph shall not apply
to (A) the Shares to be sold hereunder, (B) the issuance by the Company of
shares of Common Stock upon the exercise of an option or warrant or the
conversion of a


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security outstanding on the date hereof of which the Underwriters have been
advised in writing, (C) transactions by any person other than the Company
relating to shares of Common Stock or other securities acquired in open market
transactions after the completion of the offering of the Shares, (D) transfers
of shares of Common Stock or any securities convertible into or exercisable or
exchangeable for shares of Common Stock to a family member of the Selling
Shareholder or trust created for the benefit of the Selling Shareholder or a
family member of the Selling Shareholder, (E) transfers of shares of Common
Stock or any securities convertible into or exercisable or exchangeable for
shares of Common Stock to an affiliate of the Selling Shareholder, (F) grants of
employee stock options pursuant to the terms of a plan in effect on the date
hereof, (G) issuances of shares of Common Stock pursuant to the Company's
employee benefit plans in effect on the date hereof, (H) issuances in connection
with the merger with or acquisition of another corporation or entity or the
acquisition of the assets or properties of any such corporation or entity and
the related entry into a merger or acquisition agreement with respect to such
merger or acquisition, provided that in the case of any transfer or distribution
pursuant to clause (D), (E) or (H), (i) each transferee agrees to be bound by
the terms of this and the immediately preceding paragraph and (ii) no filing by
any party (transferee or transferor) under Section 16(a) of the Exchange Act
shall be required or shall be made voluntarily in connection with such transfer
or distribution (other than a filing on Form 5 made after the expiration of the
90-day period referred to above). In addition, the Selling Shareholder, agrees
that, without the prior written consent of Morgan Stanley & Co. Incorporated on
behalf of the Underwriters, it will not, during the period ending 90 days after
the date of the Prospectus, make any demand for, or exercise any right with
respect to, the registration of any shares of Common Stock or any security
convertible into or exercisable or exchangeable for Common Stock.

         4. TERMS OF PUBLIC OFFERING. The Sellers are advised by you that the
Underwriters propose to make a public offering of their respective portions of
the Shares as soon after the Registration Statement and this Agreement have
become effective as in your judgment is advisable. The Sellers are further
advised by you that the Shares are to be offered to the public initially at $___
a share (the "PUBLIC OFFERING PRICE") and to certain dealers selected by you at
a price that represents a concession not in excess of $____ a share under the
Public Offering Price, and that any Underwriter may allow, and such dealers may
reallow, a concession, not in excess of $___ a share, to any Underwriter or to
certain other dealers.

         5. PAYMENT AND DELIVERY. Payment for the Firm Shares to be sold by each
Seller shall be made to such Seller in Federal or other funds immediately
available in New York City against delivery of such Firm Shares for the
respective accounts of the several Underwriters at 10:00 a.m., New York City


                                       12
<Page>

time, on ____________, 2002, or at such other time on the same or such other
date, not later than _________, 2002,(1) as shall be designated in writing by
you. The time and date of such payment are hereinafter referred to as the
"CLOSING DATE."

         Payment for any Additional Shares shall be made to the Company in
Federal or other funds immediately available in New York City against delivery
of such Additional Shares for the respective accounts of the several
Underwriters at 10:00 a.m., New York City time, on the date specified in the
corresponding notice described in Section 3 or at such other time on the same or
on such other date, in any event not later than _______, 2002,(2) as shall be
designated in writing by you.

         The Firm Shares and Additional Shares shall be registered in such names
and in such denominations as you shall request in writing not later than one
full business day prior to the Closing Date or the applicable Option Closing
Date, as the case may be. The Firm Shares and Additional Shares shall be
delivered to you on the Closing Date or an Option Closing Date, as the case may
be, for the respective accounts of the several Underwriters, with any transfer
taxes payable in connection with the transfer of the Shares to the Underwriters
duly paid, against payment of the Purchase Price therefor.

         6. CONDITIONS TO THE UNDERWRITERS' OBLIGATIONS. The obligations of the
Sellers to sell the Shares to the Underwriters and the several obligations of
the Underwriters to purchase and pay for the Shares on the Closing Date are
subject to the condition that the Registration Statement shall have become
effective not later than [4:00pm] (New York City time) on the date hereof.

         The several obligations of the Underwriters are subject to the
following further conditions:

                  (a) Subsequent to the execution and delivery of this Agreement
         and prior to the Closing Date:

                           (i) there shall not have occurred any downgrading,
                  nor shall any notice have been given of any intended or
                  potential downgrading or of any review for a possible change
                  that does not indicate the direction of the possible change,
                  in the rating accorded any of the Company's or any
                  subsidiary's securities or in any subsidiary's financial
                  strength or claims-paying ability


- -----------------------
         (1) Insert date 5 business days after initial closing date.

         (2) Insert date 10 business days after the expiration of the green shoe
option.


                                       13
<Page>

                  rating by A.M. Best Company, Inc. or any other "nationally
                  recognized statistical rating organization," as such term is
                  defined for purposes of Rule 436(g)(2) under the Securities
                  Act; and

                           (ii) there shall not have occurred any change, or any
                  development involving a prospective change, in the condition,
                  financial or otherwise, or in the earnings, business or
                  operations of the Company and its subsidiaries, taken as a
                  whole, from that set forth in the Prospectus (exclusive of any
                  amendments or supplements thereto subsequent to the date of
                  this Agreement) that, in your judgment, is material and
                  adverse and that makes it, in your judgment, impracticable to
                  market the Shares on the terms and in the manner contemplated
                  in the Prospectus.

                  (b) The Underwriters shall have received on the Closing Date a
         certificate, dated the Closing Date and signed by an executive officer
         of the Company, to the effect set forth in Section 6(a)(i) above and to
         the effect that the representations and warranties of the Company
         contained in this Agreement are true and correct as of the Closing Date
         and that the Company has complied with all of the agreements and
         satisfied all of the conditions on its part to be performed or
         satisfied hereunder on or before the Closing Date.

                  The officer signing and delivering such certificate may rely
         upon the best of his or her knowledge as to proceedings threatened.

                  (c) The Underwriters shall have received on the Closing Date
         an opinion of [ ], in-house counsel for OneBeacon Insurance Group LLC,
         dated the Closing Date, substantially in the form of Exhibit A.

                  (d) The Underwriters shall have received on the Closing Date
         an opinion of [ ], in-house counsel for Folksamerica Holding Company,
         Inc., dated the Closing Date, substantially in the form of Exhibit B.

                  (e) The Underwriters shall have received on the Closing Date
         an opinion and "10b-5" statement of Cravath, Swaine & Moore, outside
         counsel for the Company, dated the Closing Date, substantially in the
         form of Exhibit C.

                  (f) The Underwriters shall have received on the Closing Date
         an opinion of Conyers Dill & Pearman, Bermuda counsel to the Company,
         dated the Closing Date, substantially in the form of Exhibit D.

                  (g) The Underwriters shall have received on the Closing Date
         an opinion of Shearman & Sterling, U.S. counsel for the Selling


                                       14
<Page>

         Shareholder, dated the Closing Date, substantially in the form of
         Exhibit E.

                  (h) The Underwriters shall have received on the Closing Date
         an opinion of Torys LLP, Canadian counsel for the Selling Shareholder,
         dated the Closing Date, substantially in the form of Exhibit F.

                  (i) The Underwriters shall have received on the Closing Date a
         disclosure statement of Davis Polk & Wardwell, counsel for the
         Underwriters, dated the Closing Date.

                  With respect to their "10b-5" or "disclosure" statements,
         Cravath, Swaine & Moore and Davis Polk & Wardwell may state that their
         beliefs are based upon their participation in the preparation of the
         Registration Statement and Prospectus and any amendments or supplements
         thereto and review and discussion of the contents thereof, but are
         without independent check or verification, except as specified. With
         respect to paragraphs 6(g) and 6(h) above, Shearman & Sterling and
         Torys LLP may rely upon an opinion or opinions of counsel for the
         Selling Shareholder and, with respect to factual matters and to the
         extent such counsel deems appropriate, upon the representations of the
         Selling Shareholder contained herein and in the Custody Agreement and
         [Power of Attorney] of the Selling Shareholder and in other documents
         and instruments; PROVIDED that (A) each such counsel for the Selling
         Shareholder is satisfactory to your counsel, (B) a copy of each opinion
         so relied upon is delivered to you and is in form and substance
         satisfactory to your counsel, (C) copies of such Custody Agreements and
         Powers of Attorney and of any such other documents and instruments
         shall be delivered to you and shall be in form and substance
         satisfactory to your counsel and (D) Shearman & Sterling and Torys LLP
         shall state in their respective opinions that they are justified in
         relying on each such other opinion.

                  The opinions of in-house counsel for One Beacon Insurance
         Group LLC and Folksamerica Holding Company, Inc., Cravath, Swaine &
         Moore (including the 10b-5 statement), Conyers Dill & Pearman, Shearman
         & Sterling and Torys LLP described above shall be rendered to the
         Underwriters at the request of the Company or the Selling Shareholder,
         as the case may be, and shall so state therein.

                  (j) The Underwriters shall have received, on each of the date
         hereof and the Closing Date, a letter dated the date hereof or the
         Closing Date, as the case may be, in form and substance satisfactory to
         the Underwriters, from PricewaterhouseCoopers LLP, independent public
         accountants the Company and for CGU Corporation each containing


                                       15
<Page>

         statements and information of the type ordinarily included in
         accountants' "comfort letters" to underwriters with respect to the
         financial statements and certain financial information contained in the
         Registration Statement and the Prospectus; PROVIDED that the letters
         delivered on the Closing Date shall use a "cut-off date" not earlier
         than the date hereof.

                  (k) The "lock-up" agreements, each substantially in the form
         of Exhibit G hereto, between you and certain shareholders, officers and
         directors of the Company relating to sales and certain other
         dispositions of shares of Common Stock or certain other securities,
         delivered to you on or before the date hereof, shall be in full force
         and effect on the Closing Date.

                  (l) The Custody Agreement shall be in full force and effect on
         the Closing Date.

         The several obligations of the Underwriters to purchase Additional
Shares hereunder are subject to the delivery to you on the applicable Option
Closing Date of such documents as you may reasonably request with respect to the
good standing of the Company, the due authorization and issuance of the
Additional Shares to be sold on such Option Closing Date and other matters
related to the issuance of such Additional Shares.

         7. COVENANTS OF THE COMPANY. In further consideration of the agreements
of the Underwriters herein contained, the Company covenants with each
Underwriter as follows:

                  (a) To furnish to you, without charge, 6 signed copies of the
         Registration Statement (including exhibits thereto and documents
         incorporated by reference) and for delivery to each other Underwriter a
         conformed copy of the Registration Statement (without exhibits thereto)
         and, during the period mentioned in Section 7(c) below, as many copies
         of the Prospectus and any supplements and amendments thereto or to the
         Registration Statement as you may reasonably request. The terms
         "supplement" and "amendment" or "amend" as used in this Agreement shall
         include all documents subsequently filed by the Company with the
         Commission pursuant to the Exchange Act that are deemed to be
         incorporated by reference in the Prospectus.

                  (b) Before amending or supplementing the Registration
         Statement or the Prospectus, to furnish to you a copy of each such
         proposed amendment or supplement and not to file any such proposed
         amendment or supplement to which you reasonably object, and to file
         with the Commission within the applicable period specified in Rule
         424(b) under the Securities Act any prospectus required to be filed
         pursuant to such Rule.


                                       16
<Page>

                  (c) If, during such period after the first date of the public
         offering of the Shares as in the opinion of counsel for the
         Underwriters the Prospectus is required by law to be delivered in
         connection with sales by an Underwriter or dealer, any event shall
         occur or condition exist as a result of which it is necessary to amend
         or supplement the Prospectus in order to make the statements therein,
         in the light of the circumstances when the Prospectus is delivered to a
         purchaser, not misleading, or if, in the opinion of counsel for the
         Underwriters, it is necessary to amend or supplement the Prospectus to
         comply with applicable law, forthwith to prepare, file with the
         Commission and furnish, at its own expense, to the Underwriters and to
         the dealers (whose names and addresses you will furnish to the Company)
         to which Shares may have been sold by you on behalf of the Underwriters
         and to any other dealers upon request, either amendments or supplements
         to the Prospectus so that the statements in the Prospectus as so
         amended or supplemented will not, in the light of the circumstances
         when the Prospectus is delivered to a purchaser, be misleading or so
         that the Prospectus, as amended or supplemented, will comply with law.

                  (d) To endeavor to qualify the Shares for offer and sale under
         the securities or Blue Sky laws of such jurisdictions as you shall
         reasonably request.

                  (e) To make generally available to the Company's security
         holders and to you as soon as practicable an earning statement covering
         the twelve-month period ending [September 30], 2003 that satisfies the
         provisions of Section 11(a) of the Securities Act and the rules and
         regulations of the Commission thereunder.

                  (f) To use the net proceeds from the offering of Shares by the
         Company pursuant to this Agreement as set forth in the Prospectus under
         the heading "Use of Proceeds".

         8. COVENANTS OF THE SELLING SHAREHOLDER. In further consideration of
the agreements of the Underwriters herein contained, the Selling Shareholder
covenants with each Underwriter as follows:

                  (a) At any time during the period described in Section 7(c)
         above, if there is any change in the information provided by such
         Selling Shareholder for use in the Registration Statement, the Selling
         Shareholder will immediately notify the Company and Morgan Stanley &
         Co. Incorporated of such change.

                  (b) The Selling Shareholder will furnish any information which
         the Company, the Underwriters or their respective counsel reasonably


                                       17
<Page>

         deems necessary or desirable in connection with the preparation and
         filing of any amendments and supplements to the Registration Statement
         or the Prospectus or any other filing with any regulatory body or
         agency (including the National Association of Securities Dealers, Inc.
         ("NASD")).

         9. EXPENSES. Whether or not the transactions contemplated in this
Agreement are consummated or this Agreement is terminated, the Company agrees to
pay or cause to be paid all expenses incident to the performance of its and the
Selling Shareholder's obligations under this Agreement, including: (i) the fees,
disbursements and expenses of the Company's counsel, the Company's accountants
and counsel for the Selling Shareholder in connection with the registration and
delivery of the Shares under the Securities Act and all other fees or expenses
in connection with the preparation and filing of the Registration Statement, any
preliminary prospectus, the Prospectus and amendments and supplements to any of
the foregoing, including all printing costs associated therewith, and the
mailing and delivering of copies thereof to the Underwriters and dealers, in the
quantities hereinabove specified, (ii) all costs and expenses related to the
transfer and delivery of the Shares to the Underwriters, including any transfer
or other taxes payable thereon, (iii) the cost of printing or producing any Blue
Sky or Legal Investment memorandum in connection with the offer and sale of the
Shares under state securities laws and all expenses in connection with the
qualification of the Shares for offer and sale under state securities laws as
provided in Section 7(d) hereof, including filing fees and the reasonable fees
and disbursements of counsel for the Underwriters in connection with such
qualification and in connection with the Blue Sky or Legal Investment
memorandum, (iv) all filing fees and the reasonable fees and disbursements of
counsel to the Underwriters incurred in connection with the review and
qualification of the offering of the Shares by the NASD, (v) all costs and
expenses incident to listing the Shares on the New York Stock Exchange, (vi) the
cost of printing certificates representing the Shares, (vii) the costs and
charges of any transfer agent, registrar or depositary, (viii) the costs and
expenses of the Company relating to investor presentations on any "road show"
undertaken in connection with the marketing of the offering of the Shares,
including, without limitation, expenses associated with the production of road
show slides and graphics, fees and expenses of any consultants engaged in
connection with the road show presentations with the prior approval of the
Company, travel and lodging expenses of the representatives and officers of the
Company and any such consultants, and the cost of any aircraft chartered in
connection with the road show, (ix) all other costs and expenses incident to the
performance of the obligations of the Company hereunder for which provision is
not otherwise made in this Section. It is understood, however, that except as
provided in this Section, Section 10 entitled "Indemnity and Contribution", and
the last paragraph of Section 12 below, the Underwriters will pay all of their
costs and expenses, including fees and disbursements of their counsel, stock
transfer taxes payable on


                                       18
<Page>

resale of any of the Shares by them and any advertising expenses connected with
any offers they may make.

         The provisions of this Section shall not supersede or otherwise affect
any agreement that the Sellers may otherwise have for the allocation of such
expenses among themselves.

         10. INDEMNITY AND CONTRIBUTION. The Company agrees to indemnify and
hold harmless each Underwriter, (i) each person, if any, who controls any
Underwriter within the meaning of either Section 15 of the Securities Act or
Section 20 of the Securities Exchange Act of 1934, as amended (the "EXCHANGE
ACT"), and each affiliate of any Underwriter within the meaning of Rule 405
under the Securities Act (each an "UNDERWRITER INDEMNIFIED PERSON") and (ii) the
Selling Shareholder and each person, if any, who controls the Selling
Shareholder within the meaning of either Section 15 of the Securities Act or
Section 20 of the Exchange Act, from and against any and all losses, claims,
damages and liabilities (including, without limitation, any legal or other
expenses reasonably incurred in connection with defending or investigating any
such action or claim) caused by any untrue statement or alleged untrue statement
of a material fact contained in the Registration Statement or any amendment
thereof, any preliminary prospectus or the Prospectus (as amended or
supplemented if the Company shall have furnished any amendments or supplements
thereto), or caused by any omission or alleged omission to state therein a
material fact required to be stated therein or necessary to make the statements
therein not misleading, except insofar as such losses, claims, damages or
liabilities are caused by any such untrue statement or omission or alleged
untrue statement or omission based upon information relating, in the case of (i)
above, to any Underwriter, or, in the case of (ii) above, the Selling
Shareholder, furnished to the Company in writing by such Underwriter through you
or by the Selling Shareholder, as the case may be, expressly for use therein.

         (b) The Selling Shareholder agrees to indemnify and hold harmless the
Company, its directors, its officers who sign the Registration Statement and
each person, if any, who controls the Company within the meaning of either
Section 15 of the Securities Act or Section 20 of the Exchange Act and each
Underwriter Indemnified Person, from and against any and all losses, claims,
damages and liabilities (including, without limitation, any legal or other
expenses reasonably incurred in connection with defending or investigating any
such action or claim) caused by any untrue statement or alleged untrue statement
of a material fact contained in the Registration Statement or any amendment
thereof, any preliminary prospectus or the Prospectus (as amended or
supplemented if the Company shall have furnished any amendments or supplements
thereto), or caused by any omission or alleged omission to state therein a
material fact required to be stated therein or necessary to make the statements
therein not misleading, but only with reference to information relating to the
Selling


                                       19
<Page>

Shareholder furnished in writing by or on behalf of the Selling Shareholder
expressly for use in the Registration Statement, any preliminary prospectus, the
Prospectus or any amendments or supplements thereto. The liability of the
Selling Shareholder under the indemnity agreement contained in this paragraph
shall be limited to an amount equal to the total net proceeds received by the
Selling Shareholder from the sale of Shares by the Selling Shareholder under
this Agreement.

         (c) Each Underwriter agrees, severally and not jointly, to indemnify
and hold harmless the Company, the Selling Shareholder, the directors of the
Company, the officers of the Company who sign the Registration Statement and
each person, if any, who controls the Company or Selling Shareholder within the
meaning of either Section 15 of the Securities Act or Section 20 of the Exchange
Act from and against any and all losses, claims, damages and liabilities
(including, without limitation, any legal or other expenses reasonably incurred
in connection with defending or investigating any such action or claim) caused
by any untrue statement or alleged untrue statement of a material fact contained
in the Registration Statement or any amendment thereof, any preliminary
prospectus or the Prospectus (as amended or supplemented if the Company shall
have furnished any amendments or supplements thereto), or caused by any omission
or alleged omission to state therein a material fact required to be stated
therein or necessary to make the statements therein not misleading, but only
with reference to information relating to such Underwriter furnished to the
Company in writing by such Underwriter through you expressly for use in the
Registration Statement, any preliminary prospectus, the Prospectus or any
amendments or supplements thereto.

         (d) In case any proceeding (including any governmental investigation)
shall be instituted involving any person in respect of which indemnity may be
sought pursuant to Section 10(a), 10(b) or 10(c), such person (the "INDEMNIFIED
PARTY") shall promptly notify the person against whom such indemnity may be
sought (the "INDEMNIFYING PARTY") in writing and the indemnifying party, upon
request of the indemnified party, shall retain counsel reasonably satisfactory
to the indemnified party to represent the indemnified party and any others the
indemnifying party may designate in such proceeding and shall pay the fees and
disbursements of such counsel related to such proceeding. In any such
proceeding, any indemnified party shall have the right to retain its own
counsel, but the fees and expenses of such counsel shall be at the expense of
such indemnified party unless (i) the indemnifying party and the indemnified
party shall have mutually agreed to the retention of such counsel or (ii) the
named parties to any such proceeding (including any impleaded parties) include
both the indemnifying party and the indemnified party and representation of both
parties by the same counsel would be inappropriate due to actual or potential
differing interests between them. It is understood that the indemnifying party
shall not, in respect of the legal expenses of any indemnified party in
connection with any


                                       20
<Page>

proceeding or related proceedings in the same jurisdiction, be liable for (i)
the fees and expenses of more than one separate firm (in addition to any local
counsel) for all Underwriters and all persons, if any, who control any
Underwriter within the meaning of either Section 15 of the Securities Act or
Section 20 of the Exchange Act or who are affiliates of any Underwriter within
the meaning of Rule 405 under the Securities Act, (ii) the fees and expenses of
more than one separate firm (in addition to any local counsel) for the Company,
its directors, its officers who sign the Registration Statement and each person,
if any, who controls the Company within the meaning of either such Section and
(iii) the fees and expenses of more than one separate firm (in addition to any
local counsel) for the Selling Shareholder and all persons, if any, who control
the Selling Shareholder within the meaning of either such Section, and that all
such fees and expenses shall be reimbursed as they are incurred. In the case of
any such separate firm for the Underwriters and such control persons and
affiliates of any Underwriters, such firm shall be designated in writing by
Morgan Stanley & Co. Incorporated. In the case of any such separate firm for the
Company, and such directors, officers and control persons of the Company, such
firm shall be designated in writing by the Company. In the case of any such
separate firm for the Selling Shareholder and such control persons of the
Selling Shareholder, such firm shall be designated in writing by Fairfax
Financial Holdings Limited. The indemnifying party shall not be liable for any
settlement of any proceeding effected without its written consent, but if
settled with such consent or if there be a final judgment for the plaintiff, the
indemnifying party agrees to indemnify the indemnified party from and against
any loss or liability by reason of such settlement or judgment. Notwithstanding
the foregoing sentence, if at any time an indemnified party shall have
requested, by registered mail with receipt confirmation requested, an
indemnifying party to reimburse the indemnified party for fees and expenses of
counsel as contemplated by the second and third sentences of this paragraph, the
indemnifying party agrees that it shall be liable for any settlement of any
proceeding effected without its written consent if (i) such settlement is
entered into more than 30 days after receipt by such indemnifying party of the
aforesaid request, as indicated by the receipt confirmation, and (ii) such
indemnifying party shall not have reimbursed the indemnified party in accordance
with such request prior to the date of such settlement. No indemnifying party
shall, without the prior written consent of the indemnified party, effect any
settlement of any pending or threatened proceeding in respect of which any
indemnified party is or could have been a party and indemnity could have been
sought hereunder by such indemnified party, unless such settlement includes an
unconditional release of such indemnified party from all liability on claims
that are the subject matter of such proceeding.

         (e) To the extent the indemnification provided for in Section 10(a),
10(b) or 10(c) is unavailable to an indemnified party or insufficient in respect
of any losses, claims, damages or liabilities referred to therein, then each
indemnifying party under such paragraph, in lieu of indemnifying such
indemnified party thereunder, shall contribute to the amount paid or payable by


                                       21
<Page>

such indemnified party as a result of such losses, claims, damages or
liabilities in such proportion as is appropriate to reflect the relative
benefits received by the indemnifying party or parties on the one hand and the
indemnified party or parties on the other hand from the offering of the Shares
or (ii) if the allocation provided by clause 10(e)(i) above is not permitted by
applicable law, in such proportion as is appropriate to reflect not only the
relative benefits referred to in clause 10(e)(i) above but also the relative
fault of the indemnifying party or parties on the one hand and of the
indemnified party or parties on the other hand in connection with the statements
or omissions that resulted in such losses, claims, damages or liabilities, as
well as any other relevant equitable considerations. The relative benefits
received by the Sellers on the one hand and the Underwriters on the other hand
in connection with the offering of the Shares shall be deemed to be in the same
respective proportions as the net proceeds from the offering of the Shares
(before deducting expenses) received by each Seller and the total underwriting
discounts and commissions received by the Underwriters, in each case as set
forth in the table on the cover of the Prospectus, bear to the aggregate Public
Offering Price of the Shares. The relative fault of the Sellers on the one hand
and the Underwriters on the other hand shall be determined by reference to,
among other things, whether the untrue or alleged untrue statement of a material
fact or the omission or alleged omission to state a material fact relates to
information supplied by the Sellers or by the Underwriters and the parties'
relative intent, knowledge, access to information and opportunity to correct or
prevent such statement or omission. As among the Company and the Selling
Shareholders, relative benefits and relative fault shall be determined on the
basis of the factors set forth in the preceding two sentences. The Underwriters'
respective obligations to contribute pursuant to this Section 10 are several in
proportion to the respective number of Shares they have purchased hereunder, and
not joint. The liability of the Selling Shareholder under the contribution
agreement contained in this paragraph shall be limited to an amount equal to the
total net proceeds from the sale of the Shares sold by the Selling Shareholder
under this Agreement.

         (f) The Sellers and the Underwriters agree that it would not be just or
equitable if contribution pursuant to this Section 10 were determined by PRO
RATA allocation (even if the Underwriters were treated as one entity for such
purpose) or by any other method of allocation that does not take account of the
equitable considerations referred to in Section 10(e). The amount paid or
payable by an indemnified party as a result of the losses, claims, damages and
liabilities referred to in the immediately preceding paragraph shall be deemed
to include, subject to the limitations set forth above, any legal or other
expenses reasonably incurred by such indemnified party in connection with
investigating or defending any such action or claim. Notwithstanding the
provisions of this Section 10, (i) no Underwriter shall be required to
contribute any amount in excess of the amount by which the total price at which
the Shares underwritten by it and distributed to the public were offered to the
public exceeds the amount of any damages that such Underwriter has otherwise
been required to pay by reason of such untrue or


                                       22
<Page>

alleged untrue statement or omission or alleged omission and (ii) the Selling
Shareholder shall not be required to contribute any amount in excess of the
amount by which the net proceeds received from the sale of Shares by the Selling
Shareholder exceeds the amount of any damages that the Selling Shareholder has
otherwise been required to pay by reason of such untrue or alleged untrue
statement or omission or alleged omission. No person guilty of fraudulent
misrepresentation (within the meaning of Section 11(f) of the Securities Act)
shall be entitled to contribution from any person who was not guilty of such
fraudulent misrepresentation. The remedies provided for in this Section 10 are
not exclusive and shall not limit any rights or remedies which may otherwise be
available to any indemnified party at law or in equity.

         (g) The indemnity and contribution provisions contained in this Section
10 and the representations, warranties and other statements of the Company and
the Selling Shareholder contained in this Agreement shall remain operative and
in full force and effect regardless of (i) any termination of this Agreement,
(ii) any investigation made by or on behalf of any Underwriter, the person
controlling any Underwriter or any affiliate of any Underwriter, any Selling
Shareholder or any person controlling the Selling Shareholder, or the Company,
its officers or directors or any person controlling the Company and (iii)
acceptance of and payment for any of the Shares.

         11. TERMINATION. The Underwriters may terminate this Agreement by
notice given by you to the Company, if after the execution and delivery of this
Agreement and prior to the Closing Date (i) trading generally shall have been
suspended or materially limited on, or by, as the case may be, any of the New
York Stock Exchange, the American Stock Exchange, the Nasdaq National Market,
the Chicago Board of Options Exchange, the Chicago Mercantile Exchange or the
Chicago Board of Trade, (ii) trading of any securities of the Company shall have
been suspended on any exchange or in any over-the-counter market, (iii) a
material disruption in securities settlement, payment or clearance services in
the United States shall have occurred, (iv) any moratorium on commercial banking
activities shall have been declared by Federal or New York State authorities or
(v) there shall have occurred any outbreak or escalation of hostilities, or any
change in financial markets, or any calamity or crisis that, in your judgment,
is material and adverse and which, singly or together with any other event
specified in this clause (v), makes it, in your judgment, impracticable or
inadvisable to proceed with the offer, sale or delivery of the Shares on the
terms and in the manner contemplated in the Prospectus.

         12. EFFECTIVENESS; DEFAULTING UNDERWRITERS. This Agreement shall become
effective upon the execution and delivery hereof by the parties hereto.

         If, on the Closing Date or an Option Closing Date, as the case may be,
any one or more of the Underwriters shall fail or refuse to purchase Shares that
it has


                                       23
<Page>

or they have agreed to purchase hereunder on such date, and the aggregate number
of Shares which such defaulting Underwriter or Underwriters agreed but failed or
refused to purchase is not more than one-tenth of the aggregate number of the
Shares to be purchased on such date, the other Underwriters shall be obligated
severally in the proportions that the number of Firm Shares set forth opposite
their respective names in Schedule II bears to the aggregate number of Firm
Shares set forth opposite the names of all such non-defaulting Underwriters, or
in such other proportions as you may specify, to purchase the Shares which such
defaulting Underwriter or Underwriters agreed but failed or refused to purchase
on such date; PROVIDED that in no event shall the number of Shares that any
Underwriter has agreed to purchase pursuant to this Agreement be increased
pursuant to this Section 12 by an amount in excess of one-ninth of such number
of Shares without the written consent of such Underwriter. If, on the Closing
Date, any Underwriter or Underwriters shall fail or refuse to purchase Firm
Shares and the aggregate number of Firm Shares with respect to which such
default occurs is more than one-tenth of the aggregate number of Firm Shares to
be purchased, and arrangements satisfactory to you, the Company and the Selling
Shareholders for the purchase of such Firm Shares are not made within 36 hours
after such default, this Agreement shall terminate without liability on the part
of any non-defaulting Underwriter, the Company or the Selling Shareholders. In
any such case either you or the relevant Sellers shall have the right to
postpone the Closing Date, but in no event for longer than seven days, in order
that the required changes, if any, in the Registration Statement and in the
Prospectus or in any other documents or arrangements may be effected. If, on an
Option Closing Date, any Underwriter or Underwriters shall fail or refuse to
purchase Additional Shares and the aggregate number of Additional Shares with
respect to which such default occurs is more than one-tenth of the aggregate
number of Additional Shares to be purchased on such Option Closing Date, the
non-defaulting Underwriters shall have the option to (i) terminate their
obligation hereunder to purchase the Additional Shares to be sold on such Option
Closing Date or (ii) purchase not less than the number of Additional Shares that
such non-defaulting Underwriters would have been obligated to purchase in the
absence of such default. Any action taken under this paragraph shall not relieve
any defaulting Underwriter from liability in respect of any default of such
Underwriter under this Agreement.

         If this Agreement shall be terminated by the Underwriters, or any of
them, because of any failure or refusal on the part of the Company or the
Selling Shareholder to comply with the terms or to fulfill any of the conditions
of this Agreement, or if for any reason the Company or the Selling Shareholder
shall be unable to perform its obligations under this Agreement, the Seller or
Sellers whose failure, refusal or inability to perform will reimburse the
Underwriters or such Underwriters as have so terminated this Agreement with
respect to themselves, severally, for all out-of-pocket expenses (including the
fees and disbursements of their counsel) reasonably incurred by such
Underwriters in connection with this Agreement or the offering contemplated
hereunder.


                                       24
<Page>

         13. APPLICABLE LAW; SUBMISSION TO JURISDICTION; APPOINTMENT OF AGENT
FOR SERVICE. (a) This Agreement shall be governed by and construed in accordance
with the internal laws of the State of New York.

         (b) Each of the Company and the Selling Shareholder irrevocably submits
to the non-exclusive jurisdiction of any New York State or United States Federal
court sitting in The City of New York over any suit, action or proceeding
arising out of or relating to this Agreement, the Prospectus, the Registration
Statement or the offering of the Shares. Each of the Company and the Selling
Shareholder irrevocably waives, to the fullest extent permitted by law, any
objection which it may now or hereafter have to the laying of venue of any such
suit, action or proceeding brought in such a court and any claim that any such
suit, action or proceeding brought in such a court has been brought in an
inconvenient forum. To the extent that the Company or the Selling Shareholder
has or hereafter may acquire any immunity from the jurisdiction of any court or
from any legal process with respect to itself or its property, such Seller
irrevocably waives, to the fullest extent permitted by law, such immunity in
respect of any such suit, action or proceeding.

         (c) (i) The Company hereby irrevocably appoints CSC United States
Corporation Company, with offices at 1013 Centre Road, Wilmington, Delaware
19805, as its agent for service of process, and (ii) the Selling Shareholders
hereby irrevocably appoints Odyssey Re Holdings Corp., with offices at 140
Broadway, 39th Floor, New York, New York 10005, as its agent for service of
process, in either case in any suit, action or proceeding described in the
preceding paragraph. Each of the Company and the Selling Shareholder agrees that
service of process in any such suit, action or proceeding may be made upon it at
the office of their respective agents. Each of the Company and the Selling
Shareholder waives, to the fullest extent permitted by law, any other
requirements of or objections to personal jurisdiction with respect thereto.
Each of the Company and the Selling Shareholder represents and warrants that
each of their respective agents has agreed to act as such Seller's agent for
service of process, and such Seller agrees to take any and all action, including
the filing of any and all documents and instruments, that may be necessary to
continue such appointment in full force and effect.

         14. COUNTERPARTS. This Agreement may be signed in two or more
counterparts, each of which shall be an original, with the same effect as if the
signatures thereto and hereto were upon the same instrument.

         15. HEADINGS. The headings of the sections of this Agreement have been
inserted for convenience of reference only and shall not be deemed a part of
this Agreement.


                                       25
<Page>

                                Very truly yours,

                                White Mountains Insurance Group Ltd.


                                By: ____________________________________________
                                    Name:
                                    Title:

                                The Selling Shareholder named in
                                   Schedule I hereto

                                By: ____________________________________________
                                    Attorney-in Fact

Accepted as of the date hereof

Morgan Stanley & Co. Incorporated
Banc of America Securities LLC
Credit Suisse First Boston Corporation
Lehman Brothers Inc.
Merrill Lynch, Pierce, Fenner & Smith Incorporated
  as representatives of the Underwriters
Acting severally on behalf of themselves and
     the several Underwriters named in
     Schedule II hereto

By: Morgan Stanley & Co. Incorporated

By: ___________________________________________
    Name:
    Title:


                                       26
<Page>


                                                                      SCHEDULE I


                                                    NUMBER OF FIRM SHARES
            SELLING SHAREHOLDER                          TO BE SOLD
- -----------------------------------------------     ---------------------
Fairfax Financial Holdings Limited.............            200,000

         Total:................................            200,000
                                                    =====================
<Page>

                                                                     SCHEDULE II

                                                        NUMBER OF FIRM SHARES
                         UNDERWRITER                      TO BE PURCHASED
- --------------------------------------------------      ---------------------
Morgan Stanley & Co. Incorporated.................
Banc of America Securities LLC....................
Credit Suisse First Boston Corporation............
Lehman Brothers Inc...............................
Merrill Lynch, Pierce, Fenner & Smith
            Incorporated..........................



                                                        ---------------------

         Total:...................................      =====================
<Page>

                                                                    SCHEDULE III

DESIGNATED SUBSIDIARIES(3)

OneBeacon Insurance Group LLC
OneBeacon Insurance Company
OneBeacon America Insurance Company
The Camden Fire Insurance Association
Homeland Insurance Company of New York
Northern Assurance Company of America
Pennsylvania General Insurance Company
National Farmers Union P&C Company
Folksamerica Holding Company, Inc.
Folksamerica Reinsurance Company





- -----------------------------------------
         (3) Subject to review.
<Page>

                                                                       EXHIBIT A



                         [OPINION OF ONEBEACON COUNSEL]


                                      A-1
<Page>

                                                                       EXHIBIT B



                        [OPINION OF FOLKSAMERICA COUNSEL]


                                      B-1
<Page>

                                                                       EXHIBIT C



                            [OPINION/LETTER OF CS&M]


                                      C-1
<Page>

                                                                       EXHIBIT D



                                [OPINION OF CD&P]


                                      D-1
<Page>

                                                                     EXHIBIT [E]



                                [OPINION OF S&S]

                     [Awaiting further input from S&S/Torys]


                                      E-1
<Page>

                                                                     EXHIBIT [F]



                             [OPINION OF TORYS LLP]


                                      F-1
<Page>

                                                                       EXHIBIT G



                            [FORM OF LOCK-UP LETTER]

                                                              ____________, 2002

Morgan Stanley & Co. Incorporated
as representative of the Underwriters
c/o      Morgan Stanley & Co. Incorporated
         1585 Broadway
         New York, NY 10036

Dear Sirs and Mesdames:

         The undersigned understands that Morgan Stanley & Co. Incorporated
("MORGAN STANLEY") proposes to enter into an Underwriting Agreement (the
"UNDERWRITING AGREEMENT") with White Mountains Insurance Group, Ltd., a Bermuda
corporation (the "COMPANY"), providing for the public offering (the "PUBLIC
OFFERING") by the several Underwriters, including Morgan Stanley (the
"UNDERWRITERS"), of __________ shares (the "OFFERED SHARES") of the Common
Shares, par value $1.00 per share, of the Company (the "COMMON SHARES").

         To induce the Underwriters that may participate in the Public Offering
to continue their efforts in connection with the Public Offering, the
undersigned hereby agrees that, without the prior written consent of Morgan
Stanley on behalf of the Underwriters, it will not, during the period commencing
on the date of the preliminary prospectus relating to the Public Offering and
ending 90 days after the date of the final prospectus relating to the Public
Offering (the "PROSPECTUS"), (1) offer, pledge, sell, contract to sell, sell any
option or contract to purchase, purchase any option or contract to sell, grant
any option, right or warrant to purchase, lend, or otherwise transfer or dispose
of, directly or indirectly, any shares of Common Shares or any securities
convertible into or exercisable or exchangeable for Common Shares, or (2) enter
into any swap or other arrangement that transfers to another, in whole or in
part, any of the economic consequences of ownership of the Common Shares,
whether any such transaction described in clause (1) or (2) above is to be
settled by delivery of Common Shares or such other securities, in cash or
otherwise. The foregoing sentence shall not apply to (a) the sale of any Offered
Shares to the Underwriters pursuant to the Underwriting Agreement, (b)
transactions relating to shares of Common Shares or other securities acquired in
open market transactions after the completion of the Public Offering, (c)
transfers of Common Shares or any securities convertible into or exercisable or
exchangeable for Common Shares to a family member of the undersigned or trust
created for the benefit of the undersigned or a family member


                                      G-1
<Page>

of the undersigned or (d) transfers of Common Shares or any securities
convertible into or exercisable or exchangeable for Common Shares to an
affiliate of the undersigned, provided that in the case of any transfer or
distribution pursuant to clause (c) or (d), (i) each transferee agrees to be
bound by the terms of this agreement and (ii) no filing by any party (transferee
or transferor) under Section 16(a) of the Securities Exchange Act of 1934 shall
be required or shall be made voluntarily in connection with such transfer or
distribution (other than a filing on Form 5 made after the expiration of the
90-day period referred to above).

         In addition, the undersigned agrees that, without the prior written
consent of Morgan Stanley on behalf of the Underwriters, it will not, during the
period commencing on the date hereof and ending 90 days after the date of the
Prospectus, make any demand for or exercise any right with respect to, the
registration of any shares of Common Shares or any security convertible into or
exercisable or exchangeable for Common Shares, except to the extent that the
undersigned has previously exercised a right of registration for Common Shares
to be sold in the Public Offering. The undersigned also agrees and consents to
the entry of stop transfer instructions with the Company's transfer agent and
registrar against the transfer of the undersigned's shares of Common Shares
except in compliance with the foregoing restrictions.

         The undersigned understands that the Company and the Underwriters are
relying upon this Lock-Up Agreement in proceeding toward consummation of the
Public Offering. The undersigned further understands that this Lock-Up Agreement
shall be binding upon the undersigned's heirs, legal representatives, successors
and assigns. This Lock-up Agreement shall lapse and become null and void if the
Public Offering has not occurred on or before November 30, 2002.

         Whether or not the Public Offering actually occurs depends on a number
of factors, including market conditions. Any Public Offering will only be made
pursuant to an Underwriting Agreement, the terms of which are subject to
negotiation between the Company and the Underwriters.

                                Very truly yours,


                                _____________________________________
                                (Name)


                                _____________________________________
                                (Address)
                                _____________________________________



                                      G-2