EXHIBIT 99(f)

                               BERKSHIRE HATHAWAY

                     PREFERRED STOCK AND WARRANTS TERM SHEET

Securities to be Issued:      Newco, a Delaware corporation and a wholly-owned
                              subsidiary of White Mountains Insurance Group,
                              Ltd., a company organized under the laws of
                              Bermuda ("WTM"), will issue to Berkshire Hathaway
                              Inc., a Delaware corporation, or an affiliate
                              ("Berkshire Hathaway"), $300 million face amount
                              of preferred stock (the "Preferred Stock"), for a
                              purchase price of $225 million. WTM will issue to
                              Berkshire Hathaway or an affiliate thereof
                              warrants to acquire 1,714,285 shares of WTM's
                              common stock at an exercise price of $175 per
                              share (the "Warrants"), for a purchase price of
                              $75 million (together with the purchase price of
                              the Preferred Stock, the "Purchase Price"). Where
                              appropriate herein the term "Berkshire Hathaway"
                              shall refer to any affiliate of Berkshire Hathaway
                              that is the holder or intended holder of the
                              Preferred Stock or the Warrants.

                              The Preferred Stock and Warrants will be issued by
                              Newco and WTM, respectively, on receipt of the
                              Purchase Price from Berkshire Hathaway on the day
                              of the closing of the acquisition by Newco of CGU
                              Corporation, a Delaware corporation ("CGU"), on
                              substantially the terms of the Stock Purchase
                              Agreement with respect to CGU in the form attached
                              hereto as Exhibit B (the "Stock Purchase
                              Agreement").

                              Newco is that corporation described in Exhibit A
                              hereto as Newco; Newco has and shall have the
                              position described in Exhibit A in the corporate
                              structure of WTM and its subsidiaries; and other
                              investors are making the investments in WTM in the
                              amounts and on the terms described in Exhibit A;
                              so that immediately following the closing the
                              corporate and capital structure of WTM and its
                              direct and indirect subsidiaries shall be as set
                              forth in Exhibit A, except for such changes in the
                              corporate and capital structure of WTM and its
                              direct and indirect subsidiaries as shall not
                              adversely affect in any material respect Berkshire
                              Hathaway.

Preferred Stock Liquidation   $300 million plus any and all past due dividends,
Preference:                   whether or not declared.

Rank:                         The Preferred Stock shall rank, with respect to
                              the payment of dividends and the distribution of
                              assets, upon liquidation or otherwise, prior to
                              all other shares of preferred stock or common
                              stock of Newco and prior to all shares of any
                              other class or series of stock of Newco.


Preferred Stock Dividend:     2.35475% cumulative dividend per quarter,
                              compounded quarterly at the same rate of 2.35475%
                              per quarter (with respect to any amounts not paid
                              when due) and payable quarterly, from the date of
                              issuance. If any dividend is not paid when due,
                              Newco shall be prohibited from paying any
                              dividends or making any distributions on its
                              common stock or on any other stock junior to the
                              Preferred Stock, and from redeeming or otherwise
                              purchasing (either directly or through any
                              subsidiary) any shares of its common stock or of
                              any other stock junior to the Preferred Stock,
                              until all past due dividends are paid in full.
                              There shall be no right of redemption of the
                              Preferred Stock or other "acceleration" right
                              triggered by Newco's failure to pay dividends on
                              the Preferred Stock. So long as any shares of the
                              Preferred Stock are outstanding, Newco shall not
                              declare or pay any dividend or distribution on its
                              common stock or repurchase any shares of its
                              common stock or of any other stock junior to the
                              Preferred Stock or make any loan to, or guarantee
                              any indebtedness of, WTM or any subsidiary of WTM
                              intermediate between WTM and Newco without the
                              written consent of the holders of a
                              majority-in-interest of the Preferred Stock unless
                              the amount of such dividend, distribution,
                              repurchase, loan or guarantee by Newco is less
                              than Newco's aggregate consolidated net income
                              (under U.S. GAAP) since January 1, 2001 minus the
                              sum of (x) the aggregate dividends and
                              distributions previously paid by Newco since
                              January 1, 2001, (y) any past due dividends then
                              due to be paid on the Preferred Stock or on other
                              equity securities besides the common stock of
                              Newco and (z) the aggregate amount of any other
                              then outstanding indebtedness (plus accrued
                              interest and other related charges) of WTM or any
                              subsidiary of WTM intermediate between WTM and
                              Newco guaranteed by or payable to Newco, provided,
                              however, that notwithstanding this restriction,
                              (1) dividends not in excess of $20.0 million (in
                              addition to any dividends paid on the Preferred
                              Stock) may be paid by Newco in each of the first
                              three years following the issuance of the
                              Preferred Stock and (2) Newco may unconditionally
                              guarantee payment (provided any demand for payment
                              in connection with amounts guaranteed must first
                              be made on WTM) of up to $50,000,000 in
                              indebtedness (plus accrued interest and other
                              related charges) of WTM or any subsidiary of WTM
                              intermediate between WTM and Newco. WTM agrees to
                              pay (if it is able) any amounts subject to any
                              such guarantee that are due to be paid.

Preferred Stock Term:         Seven years from the date of issuance.  The
                              Preferred Stock will be redeemed by Newco at the
                              end of the term for the amount of the Liquidation
                              Preference.


Preferred Stock Make Whole    Newco and Berkshire Hathaway will enter into a
Provision:                    separate agreement providing that, (a) if the
                              dividends paid or deemed paid to Berkshire
                              Hathaway on the Preferred Stock do not qualify for
                              the 70 percent dividends-received deduction as a
                              result of Newco's lack of available earnings and
                              profits, Newco will reimburse Berkshire Hathaway
                              an amount equal, on an after tax basis, to any
                              additional taxes, interest and penalties paid by
                              Berkshire Hathaway as a result of such failure to
                              qualify and as a result of such reimbursement
                              payment by Newco, and (b) if the dividends paid or
                              deemed paid to Berkshire Hathaway on the Preferred
                              Stock are extraordinary dividends within the
                              meaning of Section 1059 of the Internal Revenue
                              Code, Newco will reimburse Berkshire Hathaway an
                              amount equal, on an after tax basis, to any
                              additional taxes, interest and penalties paid by
                              Berkshire Hathaway (x) as a result of such
                              dividend being an extraordinary dividend, either
                              with respect to receipt of such extraordinary
                              dividend or Berkshire Hathaway's disposition of
                              the Preferred Stock and (y) as a result of such
                              reimbursement payment by Newco.

Preferred Stock Voting:       Non-voting (except as required by law). The
                              consent or approval of holders of no less than a
                              two-thirds majority of any shares of outstanding
                              Preferred Stock, voting as a single class, shall
                              be required prior to any amendment, alteration or
                              repeal of Newco's Certificate of Incorporation or
                              any certificate of designation related to the
                              Preferred Stock or any other alteration or change
                              to the Preferred Stock's preferences, rights,
                              powers or designations that adversely affects the
                              Preferred Stock or increases the authorized number
                              of shares of the Preferred Stock.

Preferred Stock               Transferable only to an affiliate of Berkshire
Transferability:              Hathaway. The Preferred Stock has not been and
                              will not be registered under the Securities Act of
                              1933 and may not be offered or sold in the United
                              States or to U.S. persons in the absence of such
                              registration except in reliance on an exemption
                              from the Securities Act.

Closing:                      The Transactions are anticipated to close between
                              December 15, 2000 and February 15, 2001. The drop
                              dead date for this equity commitment will match
                              the drop dead date in the Stock Purchase
                              Agreement; PROVIDED, HOWEVER, Berkshire Hathaway
                              may immediately terminate this equity commitment
                              by written notice to WTM if (a) any of the
                              conditions to Berkshire Hathaway's obligation
                              hereunder to complete the Berkshire Hathaway
                              Investment shall have become incapable of
                              fulfillment prior to June 30, 2001, and shall have
                              not been waived by Berkshire Hathaway or (b) there
                              shall be any order, injunction, or decree of any
                              governmental entity which prohibits the
                              consummation of the Berkshire Hathaway Investment
                              and such order, injunction or decree shall have
                              become final and nonappealable.


Obligations to Purchase       Berkshire Hathaway will be obligated to purchase
Preferred Stock and           the Preferred Stock and Warrants (the "Berkshire
Warrants:                     Hathaway Investment") concurrently with when the
                              Transactions (as defined in Exhibit A) are
                              completed, including the closing of the
                              acquisition by Newco of CGU pursuant to the terms
                              and conditions of the Stock Purchase Agreement,
                              the consummation of the Financing on the terms and
                              conditions set forth in the Commitment Letter
                              (each as defined in Exhibit A), the consummation
                              of the sale of the convertible preferred stock as
                              described in Exhibit E (the "WTM Equity Term
                              Sheet") and the delivery to Berkshire Hathaway of
                              the Preferred Stock and Warrants, in each case
                              reasonably reflecting the terms of this term
                              sheet. The Stock Purchase Agreement, the
                              Commitment Letter and the WTM Equity Term Sheet
                              (except to the extent necessary to provide that
                              the Required Shareholder Approval does not apply
                              to the Series A Warrants) will not be amended and
                              the closing conditions contained therein will not
                              be waived in any material respect without the
                              prior written consent of Berkshire Hathaway. In
                              addition, Berkshire Hathaway's obligation to
                              effect the Berkshire Hathaway Investment shall be
                              subject to (a) there being no change at the time
                              of closing in the corporate and capital structure
                              of WTM and its subsidiaries as set forth on
                              Exhibit A that adversely affects in any material
                              respect Berkshire Hathaway, (b) expiration or
                              termination of the waiting period, if any, under
                              the Hart-Scott-Rodino Act with respect to the
                              Berkshire Hathaway Investment, (c) receipt of all
                              necessary approvals from state insurance
                              regulators (which approvals shall permit exercise
                              of the Warrants without any further approvals
                              other than in the case of the Series B Warrants,
                              the Required Shareholder Approval) with respect to
                              the Berkshire Hathaway Investment and (d) the
                              absence of any injunction or other order of any
                              governmental authority prohibiting the
                              consummation of the Berkshire Hathaway Investment.
                              A written notice of the closing of the acquisition
                              of CGU by Newco will be delivered to Berkshire
                              Hathaway three business days before such closing
                              day, and on the closing day, prior to Berkshire
                              Hathaway's purchase, Berkshire Hathaway shall
                              receive from WTM an officer's certificate as to
                              the satisfaction of all of the conditions to
                              Berkshire Hathaway's obligations hereunder (other
                              than as to matters that are within the knowledge
                              or control of Berkshire Hathaway). Each party
                              shall use its reasonable best efforts to obtain
                              all necessary governmental and regulatory
                              approvals.

Warrant Term:                 Seven years from the date of issuance.

Exercise of Warrants:         The Warrants will be exercisable solely for cash
                              at an exercise price of $175 per share of WTM
                              common stock (the "Exercise Price"). The Warrants
                              shall be issued in two series, Series A and Series
                              B. The Series A Warrants shall entitle the holder
                              to purchase 1,170,000 shares of WTM common stock
                              and the Series B Warrants, except as described
                              below, shall entitle the holder to purchase
                              544,285 shares of WTM common stock.


                              Because the number of shares of WTM common stock
                              issuable upon exercise of the Series B Warrants
                              exceeds the threshold for requiring shareholder
                              approval pursuant to Section 312.03(c) of the New
                              York Stock Exchange Listed Company Manual (the
                              "NYSE"), the exercise of the Series B Warrants
                              will be deferred until the earlier of March 31,
                              2003 and when WTM receives the shareholder
                              approval required by the NYSE (the "Required
                              Shareholder Approval"). WTM will seek such
                              approval not later than its 2001 Annual Meeting.
                              WTM will not issue additional shares of its common
                              stock prior to obtaining the Required Shareholder
                              Approval to the extent that such issuance would
                              reduce (after taking into account any Warrant
                              Antidilution Adjustment) the number of shares of
                              common stock that WTM could issue upon the
                              exercise of any of the Series A Warrants. WTM
                              shall at all times reserve out of its authorized
                              and unissued common stock, for the sole purpose of
                              exercise of the Warrants, such number of shares as
                              shall be sufficient to effect the exercise. If WTM
                              shall be a party to a merger or other transaction
                              in which its common stock is changed into or
                              exchanged for other securities or property, as a
                              condition of such transaction adequate provision
                              shall be made so that the Warrants upon exercise
                              shall be entitled to receive the aggregate
                              consideration which the shares of common stock
                              underlying such Warrants would be changed into or
                              receive in such transaction.

                              If after March 31, 2003, the Required Shareholder
                              Approval has not been obtained at the time of the
                              exercise of any Series B Warrants, in lieu of
                              issuing WTM common stock, WTM shall pay Warrant
                              holder in cash, for each share of WTM common stock
                              to which such holder would otherwise be entitled
                              upon exercise of such Series B Warrants, an amount
                              equal to the Current Market Price of a share of
                              WTM common stock. Any cash payment by WTM to a
                              Warrant holder pursuant to this provision shall be
                              made by WTM 90 days after notice of the exercise
                              the Warrants has been given to WTM by Warrant
                              holder.

                              "Current Market Price" shall mean, with respect to
                              each share of WTM common stock receivable upon
                              exercise of a Series B Warrant, the difference
                              between (i) the average of the closing price of a
                              share of WTM common stock on the New York Stock
                              Exchange, Inc., for the ten consecutive trading
                              days immediately prior to the date Warrant holder
                              gives written notice of its election to exercise
                              such Series B Warrant and (ii) the Exercise Price.

Call Option on Warrants:      After the fourth anniversary of the issuance of
                              the Warrants, WTM may, at its option on one or
                              more occasions, call all of the then outstanding
                              Warrants for cash in an aggregate amount equal to
                              $60 million (assuming all Warrants are
                              outstanding) or any portion of the Warrants for a
                              ratable share of the $60 million purchase price.
                              Following notice of any call, the Warrant holder
                              shall have at least 30 days to exercise any
                              Warrants covered by such call before such Warrants
                              are purchased pursuant to such call.


Warrant Registration Rights:  After the exercise of the Warrants, Warrant holder
                              will have (i) two demand registration rights in
                              aggregate and (ii) unlimited incidental
                              ("piggyback") registration rights with respect to
                              the WTM common stock received upon exercise,
                              subject to customary pro rata "cut-backs" with WTM
                              and any other selling equityholders at the
                              discretion of a managing underwriter, provided,
                              however, Warrant holder will not be subject to any
                              such "cut-backs" with respect to a registration
                              occasioned by its own demand. No other holder of
                              WTM common stock will be granted any superior
                              registration rights to those held by Berkshire
                              Hathaway, provided that Berkshire Hathaway
                              acknowledges that the Equity Partners and CGNU
                              will have the registration rights set forth in
                              Exhibit E and Exhibit D, respectively. WTM will
                              pay the registration expenses in connection with
                              any such demand and piggyback rights other than
                              any underwriting discounts and fees.
                              Notwithstanding the foregoing, WTM will not be
                              obligated to register WTM common stock which could
                              be sold under Rule 144(k).

Warrant Antidilution          With respect to any unexercised Warrants, Warrant
Adjustment:                   holder will be entitled to a customary
                              antidilution adjustment to the Exercise Price
                              and/or the number of shares of WTM common stock to
                              which the Warrants apply in the event WTM issues
                              warrants, options or other rights to purchase or
                              otherwise acquire additional stock or securities
                              convertible into or exchangeable for additional
                              WTM common stock at a price per share less than
                              fair market value or issues or sells WTM common
                              stock at a price per share less than fair market
                              value or in the event of stock splits, stock
                              dividends, certain extraordinary distributions or
                              dividends, or reorganizations. Berkshire Hathaway
                              acknowledges that the Equity Partners will be
                              issued convertible preferred stock by WTM,
                              convertible into WTM common stock, in connection
                              with the Transactions on the terms set forth in
                              Exhibit E, that CGNU may be issued WTM common
                              stock on the terms set forth in Exhibit D and that
                              Berkshire Hathaway shall not be entitled to any
                              antidilution adjustment for any such issuance or
                              conversion.

Warrant Transferability:      Nontransferable except to one or more affiliates
                              of Berkshire Hathaway.

WTM Common Stock              Transferable only in accordance with applicable
Transferability               law. The WTM common stock has not been registered
                              under the Securities Act of 1933 and may not be
                              offered or sold in the United States or to U.S.
                              persons in the absence of such registration except
                              in reliance on an exemption from the Securities
                              Act.


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                                                                       Exhibit A

Transactions:                 WTM is proposing to acquire the outstanding
                              capital stock of CGU Corporation, a Delaware
                              corporation ("CGU") and an indirect wholly owned
                              subsidiary of CGNU plc, for approximately $2.17
                              billion of which approximately $1.96 billion is
                              payable in cash and $210 million is payable with a
                              seller's note (see below). In addition, at the
                              time of the acquisition, an approximately $500
                              million note between CGU and CGNU plc will be
                              outstanding, after the reduction of the note by
                              the proceeds from the sale of Pilot, CGNU's life
                              insurance subsidiaries and certain other assets to
                              CGNU plc, as described below.

                              WTM has formed TACK Holding Corp., a Delaware
                              corporation ("Holdco"), to hold all the equity
                              interests in TACK Acquisition Corp., a Delaware
                              corporation ("Newco"), which was formed by WTM to
                              acquire CGU.

                              At the closing, the following transactions (the
                              "Transactions") shall occur:

                              Newco will acquire CGU on substantially the terms
                              of the Stock Purchase Agreement in the form
                              attached hereto as Exhibit B (the "Stock Purchase
                              Agreement");

                              CGU will sell Pilot to CGNU for approximately $285
                              million;

                              Newco will issue Newco common stock to Holdco, and
                              Holdco will issue Holdco common stock to WTM, for
                              $725 million in cash contributed by WTM to Holdco
                              and by Holdco to Newco;

                              WTM will issue not less than $300 million face
                              amount of WTM convertible preferred stock on
                              substantially the terms set forth in Exhibit E;

                              Newco will issue Newco common stock to Holdco, and
                              Holdco will issue Holdco common stock to WTM, for
                              approximately $725 million in net tangible assets
                              (Folksamerica, Peninsula, Main Street America,
                              American Centennial Insurance Company and British
                              Insurance Company of Cayman) contributed by WTM to
                              Holdco and by Holdco to Newco; these assets then
                              will be contributed by Newco to CGU;

                              Newco will borrow $1 billion pursuant to the terms
                              and conditions of a commitment letter (the
                              "Commitment Letter") from Lehman Brothers Inc.
                              substantially in the form attached hereto as
                              Exhibit C (the "Financing");




                                                                               3


                              Holdco will issue a seller's note for $210 million
                              (the "Seller's Note") on the terms set forth in
                              the term sheet attached hereto as Exhibit D to be
                              repaid in cash or in WTM Common Stock, at Holdco's
                              option, six months after closing; if repaid in WTM
                              Common Stock, the stock will be priced at $174.50
                              per share; and

                              In exchange for a purchase price of $225 million,
                              Berkshire Hathaway, Inc. will purchase Newco
                              preferred stock; in addition, for a purchase price
                              of $75 million(1) Berkshire Hathaway Inc. will
                              purchase a warrant to purchase WTM common stock.

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     (1) This $75 million is included in the $725 million cash capital
contribution by WTM to Holdco and by Holdco to Newco, described above.