LASALLE STOCK OPTION AGREEMENT

                  STOCK  OPTION  AGREEMENT,  dated as of December  19, 1999 (the
"Agreement")  by  and  between  Trenwick  Group  Inc.,  a  Delaware  corporation
("Trenwick"  or the  "Issuer"),  and  LaSalle  Re  Holdings  Limited,  a company
organized under the laws of Bermuda ("LaSalle").

                  WHEREAS,  concurrently with the execution and delivery of this
Agreement,  LaSalle,  LaSalle Re Limited,  a company organized under the laws of
Bermuda,  Trenwick,  Trenwick Group (Delaware) Inc., a Delaware  corporation and
Gowin Holdings  International  Limited,  a company  organized  under the laws of
Bermuda ("New Holdings"), are entering into an Agreement, Scheme of Arrangement,
Plan of  Merger  and Plan of  Reorganization  dated as of the date  hereof  (the
"Business Combination Agreement"); and

                  WHEREAS, as a condition to LaSalle's willingness to enter into
the Business Combination  Agreement,  LaSalle has requested that Trenwick agree,
and  Trenwick  has so agreed,  to grant to LaSalle an option to  purchase  up to
3,462,164 shares of   common  stock,  par value  $0.10 per  share,  of  Trenwick
("Trenwick Common Stock"),  together with any associated rights under the Rights
Agreement  dated as of  September  24, 1997 between  Trenwick and First  Chicago
Trust Company of New York  ("Trenwick  Common  Stock"),  in accordance  with the
terms and subject to the conditions set forth herein.

                  NOW,  THEREFORE,  to induce LaSalle to enter into the Business
Combination  Agreement,  and in  consideration  of the  foregoing and the mutual
representations,  warranties,  covenants and  agreements set forth herein and in
the  Business  Combination  Agreement,  the  parties  hereto  agree as  follows.
Capitalized  terms used herein but not defined  herein  shall have the  meanings
ascribed to them in the Business Combination Agreement.

                  1. Grant of Option.  Subject to the terms and  conditions  set
forth  herein,  Trenwick  hereby  grants to LaSalle an  irrevocable  option (the
"Trenwick Option") to purchase up to 3,462,164 (as adjusted as set forth herein)
shares (the  "Option  Shares") of Trenwick  Common  Stock (such number of Option
Shares representing 19.9% of the Trenwick Common Stock issued and outstanding on
the date hereof) in the manner set forth below at a price (the "Exercise Price")
of $18.04 per Option Share (which price per share is equal to the average of the
last  sale  prices  of  Trenwick  Common  Stock  on the ten  (10)  trading  days
immediately prior to the date of public announcement of the Business Combination
Agreement  payable in cash or by cashless  exercise in accordance with Section 4
hereof.  Notwithstanding  the foregoing,  in no event shall the number of Option
Shares for which the Trenwick  Option is exercisable  exceed 19.9% of the number
of issued and outstanding shares of Trenwick Common Stock.




                  2. Exercise of Option. The Trenwick Option may be exercised by
LaSalle,  in whole  or in  part,  at any  time or from  time to time  after  the
Business Combination Agreement becomes terminable by LaSalle under circumstances
which would or could  entitle  LaSalle to receive the Trenwick  Termination  Fee
pursuant to Section  7.4(b) of the  Business  Combination  Agreement (a "Trigger
Event")  (regardless of whether the Business  Combination  Agreement is actually
terminated or whether there occurs a closing  involving  LaSalle).  In the event
LaSalle  wishes to  exercise  the  Trenwick  Option,  LaSalle  shall  deliver to
Trenwick a written notice (an "Exercise Notice")  specifying the total number of
Option  Shares it wishes to purchase,  and specify  whether such  exercise is in
cash or by cashless  exercise in accordance with Section 4 hereof.  Each closing
of a purchase of Option Shares (an "Option Closing") shall occur, but subject to
the satisfaction or waiver of the conditions set forth in Section 3 hereof, at a
place,  on a date and at a time  designated  by  LaSalle in an  Exercise  Notice
delivered  at least  two (2)  business  days  prior  to the  date of the  Option
Closing.  The  Trenwick  Option  shall  terminate  upon the  earlier of: (i) the
Effective Time; (ii) the termination of the Business Combination Agreement other
than under  circumstances  which also  constitute a Trigger Event;  or (iii) the
180th day  following a Trigger  Event (or if, at the  expiration of such 180 day
period the  Trenwick  Option  cannot be  exercised  by reason of any  applicable
judgment,  decree,  order, law or regulation,  ten (10) business days after such
impediment  to exercise  shall have been  removed or shall have become final and
not subject to appeal,  but in no event  under this clause  (iii) later than the
365th day following such Trigger  Event).  Notwithstanding  the  foregoing,  the
Trenwick  Option may not be exercised if LaSalle is in material breach of any of
its representations or warranties, or in material breach of any of its covenants
or  agreements,  contained  in this  Agreement  or in the  Business  Combination
Agreement. Upon the giving by LaSalle to Trenwick of the Exercise Notice and the
tender  of  the  applicable   aggregate  Exercise  Price,  but  subject  to  the
satisfaction or waiver of the conditions set forth in Section 3 hereof,  LaSalle
shall be deemed to be the holder of record of the Option  Shares  issuable  upon
such exercise,  notwithstanding  that the stock transfer books of Trenwick shall
then be closed or that  certificates  representing  such Option Shares shall not
then be actually delivered to LaSalle.

                  3. Conditions to Closing.  The obligation of Trenwick to issue
the Option  Shares to LaSalle  hereunder  is  subject to the  conditions,  which
(other than the  conditions  described in clauses (i), (iii) and (iv) below) may
be waived by Trenwick in its sole discretion,  that (i) all waiting periods,  if
any,  under  the HSR  Act,  applicable  to the  issuance  of the  Option  Shares
hereunder  shall have expired or have been  terminated;  (ii) the Option  Shares
shall  have  been  approved  for  listing  on the NYSE upon  official  notice of
issuance;  (iii)  all  consents,  approvals,  orders  or  authorizations  of, or
registrations,  declarations  or  filings  with,  any  federal,  state  or local
administrative   agency  or  commission  or  other   federal,   state  or  local
Governmental  Authority,  including  without  limitation,  the Bermuda  Monetary
Authority, if any, required in connection with the issuance of the Option Shares
hereunder  shall  have  been  obtained  or made,  as the case may be  including,
without limitation,  by LaSalle; and (iv) no preliminary or permanent injunction
or  other  order  or  decree  by any  court of  competent  jurisdiction,  law or
regulation  prohibiting  or  otherwise  restraining  such  issuance  shall be in
effect.


                                       2



                  4. Payment and Delivery of Certificates.

                  (a) At any Option Closing,  LaSalle  shall pay to Trenwick the
aggregate  purchase price (equal to the Exercise Price  multiplied by the number
of Option  Shares to be  purchased  at such  Option  Closing)  for the shares of
Trenwick Common Stock purchased  pursuant to the exercise of the Trenwick Option
in immediately  available funds by wire transfer to a bank account designated in
writing by Trenwick;  provided,  however, that failure or refusal of Trenwick to
designate such account shall not preclude  LaSalle from  exercising the Trenwick
Option.  At LaSalle's  option,  in lieu of delivering  the cash Exercise  Price,
LaSalle may instruct  Trenwick in writing to deduct from the number of shares of
Trenwick  Common  Stock that would  otherwise  be issued upon such  exercise,  a
number of shares of Trenwick  Common Stock equal to the quotient  obtained  from
dividing:

                  (x) the  product  obtained  by  multiplying  (1) the number of
         shares of Trenwick  Common Stock for which the Trenwick Option is being
         exercised and (2) the Exercise Price then in effect, by

                  (y) the Fair Market Value of a share of Trenwick Common Stock.

"Fair Market Value" shall have the meaning specified in Section 12(b)(v).

                  (b) At any Option Closing, simultaneously with the delivery of
immediately  available funds as provided in Section 4(a),  Trenwick will deliver
to  LaSalle a  certificate  or  certificates  representing  the number of Option
Shares to be purchased by LaSalle at such Option  Closing,  which Option  Shares
will be free and clear of all liens,  claims,  charges and  encumbrances  of any
kind  whatsoever  and if the option is  exercised in part only,  Trenwick  shall
deliver a new option  evidencing  the rights of LaSalle  thereof to purchase the
balance of the shares  purchasable  hereunder  and (ii)  LaSalle will deliver to
Trenwick a copy of this  Agreement  and a letter  agreeing that LaSalle will not
offer to sell or otherwise dispose of such shares in violation of applicable law
or the provisions of this Agreement. If at the time of issuance of Option Shares
pursuant  to an  exercise  of the  option  hereunder,  Trenwick  shall  not have
redeemed the Trenwick Rights, or shall have issued any similar securities,  then
each Option Share issued  pursuant to such exercise will also  represent  such a
corresponding  Trenwick Right or new rights with terms substantially the same as
and at least as  favorable  to LaSalle as are  provided in the  Trenwick  Rights
Agreement or similar agreement then in effect.  Trenwick shall pay all expenses,
and any and all United States  federal,  state and local taxes and other charges
that may be payable in connection  with the  preparation,  issue and delivery of
stock  certificates under this Section 4 in the name of LaSalle or its designee.
Trenwick  shall use its  reasonable  best efforts to cause the  Trenwick  Common
Stock being  delivered  at the Option  Closing to be approved for listing on the
NYSE and shall pay all expenses in connection  with the application for approval
and the listing of such shares.



                                       3



                  5. Representations and Warranties of Trenwick. Trenwick hereby
represents  and  warrants to LaSalle  that (a)  Trenwick is a  corporation  duly
organized,  validly existing and in good standing under the laws of the State of
Delaware and has the corporate power and authority to enter into this Agreement,
(b)  the  execution  and  delivery  of  this   Agreement  by  Trenwick  and  the
consummation by Trenwick of the transactions  contemplated hereby have been duly
authorized  by all  necessary  corporate  action on the part of Trenwick  and no
other  corporate  proceedings on the part of Trenwick are necessary to authorize
this  Agreement  or  any of  the  transactions  contemplated  hereby,  (c)  this
Agreement has been duly executed and delivered by Trenwick,  constitutes a valid
and binding  obligation of Trenwick and,  assuming this Agreement  constitutes a
valid and binding  obligation of LaSalle,  is  enforceable  against  Trenwick in
accordance with its terms, (d) Trenwick has taken all necessary corporate action
to authorize  and reserve for issuance and to permit it to issue,  upon exercise
of the  Trenwick  Option,  and at all times  from the date  hereof  through  the
expiration of the Trenwick Option will have reserved,  3,462,164  authorized and
unissued  Option Shares,  such amount being subject to adjustment as provided in
Section 9, all of which, upon their issuance and delivery in accordance with the
terms of this Agreement,  will be validly issued,  fully paid and nonassessable,
(e) upon  delivery  of the Option  Shares to LaSalle  upon the  exercise  of the
Trenwick  Option,  LaSalle will acquire the Option  Shares free and clear of all
claims,  liens,  charges,  encumbrances  and  security  interests  of any nature
whatsoever,  (f) none of Trenwick, any of its affiliates or anyone acting on its
or their  behalf has  issued,  sold or offered  any  security of Trenwick to any
person under  circumstances that would cause the issuance and sale of the Option
Shares,  as contemplated by this  Agreement,  to be subject to the  registration
requirements of the Securities Act as in effect on the date hereof and, assuming
the  representations  of LaSalle  contained in Section 6(d) are true and correct
and based on LaSalle's commitment in its letter referred to in Section 4 hereof,
the issuance,  sale and delivery of the Option Shares  hereunder would be exempt
from the  registration  and prospectus  delivery  requirements of the Securities
Act,  as in effect on the date hereof  (and  Trenwick  shall not take any action
which would cause the issuance, sale and delivery of the Option Shares hereunder
not to be exempt from such requirements),  and (g) the execution and delivery of
this Agreement by Trenwick does not, and,  subject to compliance with applicable
law, the consummation by Trenwick of the transactions  contemplated  hereby will
not,  violate,  conflict  with,  or result in a breach of any  provision  of, or
constitute a default (with or without notice or a lapse of time, or both) under,
or result in the termination  of, or accelerate the performance  required by, or
result  in  a  right  of  termination,  cancellation,  or  acceleration  of  any
obligation or the loss of a material  benefit under,  or the creation of a lien,
pledge,  security  interest or other  encumbrance on assets (any such violation,
conflict,  breach,  default,  termination,  acceleration,  right of termination,
cancellation or acceleration,  loss, or creation,  a "Violation") of Trenwick or
any of its subsidiaries,  pursuant to (i) any provision of the Trenwick By-Laws,
(ii) any provision of any material  loan or credit  agreement,  note,  mortgage,
indenture,  lease,  benefit  plan or other  agreement,  obligation,  instrument,
permit, concession,  franchise or license (a "Material Contract") of Trenwick or
any of its  subsidiaries  or to which  any of them is a party or by which any of
them or their  properties  or assets are bound,  or (iii) any  judgment,  order,
decree,  statute,  law, ordinance,  rule or regulation applicable to Trenwick or
any of its subsidiaries or any of their respective  properties or assets,  which
Violation,  in the case of each of clauses  (ii) or (iii),  would have  Material
Adverse Effect on Trenwick.

                                       4



                  6.   Representations   and  Warranties  of  LaSalle.   LaSalle
represents  and  warrants  to  Trenwick  that  (a)  LaSalle  is a  company  duly
organized,  validly  existing and in good standing under the laws of Bermuda and
has the corporate  power and authority to enter into this Agreement and to carry
out its obligations hereunder,  (b) the execution and delivery of this Agreement
by LaSalle  and the  consummation  by LaSalle of the  transactions  contemplated
hereby have been duly authorized by all necessary  corporate  action on the part
of  LaSalle  and no  other  corporate  proceedings  on the part of  LaSalle  are
necessary to authorize  this Agreement or any of the  transactions  contemplated
hereby,  (c) this  Agreement has been duly executed and delivered by LaSalle and
constitutes  a valid and binding  obligation  of  LaSalle,  and,  assuming  this
Agreement constitutes a valid and binding obligation of Trenwick, is enforceable
against LaSalle in accordance with its terms, and (d) any Option Shares acquired
upon exercise of the Trenwick Option will be acquired for LaSalle's own account,
for  investment  purposes  only and will not be, and the Trenwick  Option is not
being,  acquired by LaSalle  with a view to the public  distribution  thereof in
violation  of any  applicable  provision  of the  Securities  Act,  and  (e) the
execution and delivery of this  Agreement by LaSalle does not,  and,  subject to
compliance with applicable law, the  consummation by LaSalle of the transactions
contemplated hereby will not, violate, conflict with, or result in the breach of
any provision of, or constitute a default (with or without  notice or a lapse of
time,  or both)  under,  or result in any  Violation  by  LaSalle  or any of its
subsidiaries,  pursuant to (i) any provision of the memorandum of association or
bye-laws  of  LaSalle,  (ii) any  Material  Contract  of  LaSalle  or any of its
subsidiaries  or to which  any of them is a party or by which any of them or any
of their properties or assets are bound, or (iii) any judgment,  order,  decree,
statute,  law, ordinance,  rule or regulation  applicable to LaSalle, any of its
subsidiaries or any of their respective  properties or assets,  which Violation,
in the case of each of clauses  (ii) or (iii),  would  have a  Material  Adverse
Effect on LaSalle.

                  7.   Restrictions on Transfer.

                  (a)  Restrictions on Transfer.  Prior to the first anniversary
of the  date on  which  LaSalle  purchases  any  Option  Shares  hereunder  (the
"Expiration Date"),  LaSalle shall not, directly or indirectly,  by operation of
law or otherwise,  sell, assign, pledge, or otherwise dispose of or transfer any
Option  Shares  acquired  by LaSalle  pursuant  to this  Agreement  ("Restricted
Shares")  beneficially  owned by it, other than in accordance with Section 7(b),
7(c) or  Section  8.  Subsequent  to the  Expiration  Date,  LaSalle  shall not,
directly or indirectly,  by operation of law or otherwise,  sell, assign, pledge
or otherwise dispose of or transfer any Restricted Shares  beneficially owned by
it  to  any  purchaser,   assignee,  pledgee  or  other  transferee  who  would,
immediately  after such  sale,  assignment,  pledge,  disposition  or  transfer,
beneficially  own more than  4.9% of the then  outstanding  voting  power of the
Issuer of the Restricted Shares, except in accordance with Section 7(b), 7(c) or
Section 8 and other than in market transactions at prevailing prices.

                                       5



                  (b) Permitted Sales. Following the termination of the Business
Combination  Agreement,  LaSalle  shall be  permitted  to sell or  transfer  any
Restricted  Shares  beneficially  owned by it if such sale is made pursuant to a
tender or exchange  offer or merger that has been  approved or  recommended,  or
otherwise determined to be fair to and in the best interests of the shareholders
of Trenwick,  by a majority of the members of the Board of Directors of Trenwick
(which  majority shall include a majority of directors who were directors  prior
to the announcement of such tender or exchange offer or merger).

                  (c)  Trenwick's Right of First Refusal.  At any time after the
first  occurrence of a Trigger Event and prior to the  expiration of twenty-four
(24) months  immediately  following the first purchase of Trenwick  Common Stock
pursuant  to the  Trenwick  Option,  if LaSalle  shall  desire to sell,  assign,
transfer or  otherwise  dispose of any shares of Trenwick  Common Stock or other
securities  acquired by it pursuant to the Trenwick  Option,  LaSalle shall give
Trenwick written notice of the proposed  transaction (a "LaSalle Offer Notice"),
identifying the proposed transferee, accompanied by a copy of a binding offer to
purchase  such  Trenwick  Common  Stock  or  other  securities  signed  by  such
transferee  and setting forth the terms of the proposed  transaction.  A LaSalle
Offer  Notice  shall be deemed an offer by  LaSalle to  Trenwick,  which must be
accepted,  if at all,  within  five (5)  business  days of the  receipt  of such
LaSalle Offer Notice,  on the same terms and conditions and at the same price at
which  LaSalle is  proposing  to transfer  such  Trenwick  Common Stock or other
securities  to such  transferee.  The purchase of any  Trenwick  Common Stock or
other  securities by Trenwick  shall be settled within five (5) business days of
the date of the  acceptance of the offer and the purchase price shall be paid to
LaSalle in immediately  available  funds. In the event of the failure or refusal
of Trenwick to purchase  all of the Trenwick  Common  Stock or other  securities
covered by a LaSalle Offer Notice,  LaSalle may sell all, but not less than all,
of such Trenwick Common Stock or other securities to the proposed  transferee at
a price no less than the price  specified and on terms no more  favorable to the
transferee  than those set forth in the LaSalle Offer Notice;  provided that the
provisions  of this  sentence  shall not limit the rights  LaSalle may otherwise
have in the event Trenwick has accepted the offer contained in the LaSalle Offer
Notice and  wrongfully  refuses to purchase the  Trenwick  Common Stock or other
securities  subject  thereto.  The  requirements  of this Section 7(c) shall not
apply to (i) any disposition as a result of which the proposed  transferee would
not  beneficially  own more than three  percent (3%) of the  outstanding  voting
power of  Trenwick,  (ii) any  disposition  of  Trenwick  Common  Stock or other
securities  by a person  to whom  LaSalle  has  assigned  its  rights  under the
Trenwick  Option  with the  consent  of  Trenwick,  (iii) any sale by means of a
public offering  registered  under the Securities Act, or (iv) any transfer to a
wholly-owned  subsidiary  of LaSalle  which agrees in writing to be bound by the
terms hereof.

                                       6



                  8.   Registration  Rights.  Following the  termination  of the
Business Combination Agreement, but not later than the second anniversary of the
last date that LaSalle acquired Option Shares under this Agreement,  LaSalle may
by written notice (the "Registration  Notice") to Trenwick  ("Trenwick") request
Trenwick to register  under the Securities Act all or any part of the Restricted
Shares beneficially owned by LaSalle (the "Registrable  Securities") pursuant to
a bona fide firm  commitment  underwritten  public offering in which LaSalle and
the  underwriters  shall  effect  as wide a  distribution  of  such  Registrable
Securities  as is  reasonably  practicable  and  shall  use  their  commercially
reasonable  efforts to prevent any person  (including any Group (as used in Rule
13d-5 under the Exchange Act)) and its affiliates from  purchasing  through such
offering  Restricted  Shares  representing  more  than one  percent  (1%) of the
outstanding  shares of common  stock of  Trenwick  on a fully  diluted  basis (a
"Permitted  Offering").  The  Registration  Notice shall  include a  certificate
executed by LaSalle and its proposed  managing  underwriter,  which  underwriter
shall be an  investment  banking firm of  nationally  recognized  standing  (the
"Manager"),  stating  that (i) they  have a good  faith  intention  to  commence
promptly a Permitted  Offering and (ii) the Manager in good faith believes that,
based  on the then  prevailing  market  conditions,  it will be able to sell the
Registrable  Securities  at a per share price equal to at least  eighty  percent
(80%) of the then Fair Market Value (as defined below) of such shares.  Trenwick
(and/or any person  designated  by  Trenwick)  shall  thereupon  have the option
exercisable by written notice delivered to LaSalle within five (5) business days
after the receipt of the Registration  Notice,  irrevocably to agree to purchase
all or any part of the Registrable Securities proposed to be so sold for cash at
a  price  (the  "Option  Price")  equal  to the  product  of (i) the  number  of
Registrable  Securities  to be so  purchased  by Trenwick and (ii) the then Fair
Market Value of such shares.  Any such  purchase of  Registrable  Securities  by
Trenwick (or its designee) hereunder shall take place at a closing to be held at
the principal  executive offices of Trenwick or at the offices of its counsel at
any reasonable date and time designated by Trenwick and/or such designee in such
notice  within  twenty (20)  business  days after  delivery of such notice.  Any
payment for the shares to be purchased  shall be made by delivery at the time of
such closing of the Option Price in immediately available funds. As used herein,
the "Fair Market  Value" of any share shall be the average of the daily  closing
sales  price for such share on the NYSE  during the ten (10) NYSE  trading  days
immediately preceding the date such Fair Market Value is to be determined.

                  If Trenwick does not elect to exercise its option  pursuant to
this  Section 8 with  respect to all  Registrable  Securities,  it shall use its
commercially  reasonable  efforts to effect,  as  promptly as  practicable,  the
registration under the Securities Act of the unpurchased  Registrable Securities
proposed  to be so sold;  provided,  however,  that  (i)  LaSalle  shall  not be
entitled to more than an  aggregate  of two  effective  registration  statements
hereunder and (ii)  Trenwick will not be required to file any such  registration
statement  during any period of time (not to exceed  ninety (90) days after such
request in the case of clauses  (A),  (B) or (C) below) when (A)  Trenwick is in
possession of material non-public information which it reasonably believes would
be  detrimental  to be  disclosed at such time and, in the opinion of counsel to
Trenwick,  such  information  would  have  to  be  disclosed  if a  registration
statement were filed at that time; (B) Trenwick is required under the Securities



                                       7



Act to include audited financial  statements for any period in such registration
statement and such  financial  statements are not yet available for inclusion in
such  registration  statement;  or (C) Trenwick  determines,  in its  reasonable
judgment, that such registration would interfere with any financing, acquisition
or other  material  transaction  involving  Trenwick  or any of its  affiliates.
Trenwick  shall  use its  reasonable  best  efforts  to  cause  any  Registrable
Securities  registered pursuant to this Section 8 to be qualified for sale under
the securities or blue sky laws of such  jurisdictions as LaSalle may reasonably
request and shall continue such  registration or qualification in effect in such
jurisdiction;  provided, however, that Trenwick shall not be required to qualify
to do business in, or consent to general service of process in, any jurisdiction
by reason of this provision.

                  The  registration  rights  set  forth  in this  Section  8 are
subject  to  the  condition  that  LaSalle  shall  provide  Trenwick  with  such
information with respect to such holder's Registrable Securities,  the plans for
the distribution thereof, and such other information with respect to such holder
as, in the reasonable  judgment of counsel for Trenwick,  is necessary to enable
Trenwick to include in such  registration  statement all material facts required
to be disclosed with respect to a registration thereunder.

                  A registration effected under this Section 8 shall be effected
at Trenwick's expense, except for underwriting discounts and commissions and the
fees and the expenses of counsel to LaSalle,  and Trenwick  shall provide to the
underwriters such documentation (including certificates, opinions of counsel and
"comfort"   letters  from   auditors)  as  are  customary  in  connection   with
underwritten  public offerings as such underwriters may reasonably  require.  In
connection with any such  registration,  the parties agree (i) to indemnify each
other and the  underwriters in the customary manner (provided that LaSalle shall
only be required to indemnify other parties to such  underwriting  agreement for
information  relating to such LaSalle and  supplied by it for  inclusion in such
registration  statement),  (ii) to enter into an underwriting  agreement in form
and substance  customary for  transactions of such type with the Manager and the
other underwriters  participating in such offering and (iii) to take all further
actions which shall be reasonably necessary to effect such registration and sale
(including,  if the  Manager  deems it  necessary,  participating  in road  show
presentations).

                  Trenwick  shall  be  entitled  to  include  (at  its  expense)
additional  shares of its common stock in a  registration  effected  pursuant to
this  Section  8 only if and to the  extent  the  Manager  determines  that such
inclusion will not adversely affect the prospects for success of such offering.

                   9.  Adjustment  upon Changes in  Capitalization.  (a) Without
limitation to any restriction on Trenwick  contained in this Agreement or in the
Business  Combination  Agreement,  in the event of any change in Trenwick Common
Stock  by  reason  of  stock  dividends,   split-ups,  mergers,   amalgamations,
recapitalizations,  subdivisions,  conversions, combinations, exchange of shares
or the like, the type and number of shares or securities subject to the Trenwick
Option,  and the Exercise Price per Option Share provided in Section 1, shall be
adjusted appropriately to restore to LaSalle its rights hereunder, including the
right to  purchase  from the  Trenwick  (or its  successors)  shares of Trenwick
Common Stock representing 19.9% of the outstanding Trenwick Common Stock for the
aggregate Exercise Price calculated as of the date of this Agreement as provided
in Section 1.


                                       8



                  (b) In the event that Trenwick  shall enter into an agreement:
(i) to consolidate with merge or amalgamate into any person,  other than LaSalle
or one of its  subsidiaries,  and  shall  not  be the  continuing  or  surviving
corporation of such  consolidation,  merger or amalgamation;  (ii) to permit any
person,  other than LaSalle or one of its  subsidiaries,  to merge or amalgamate
into Trenwick and Trenwick  shall be the  continuing  or surviving  corporation,
but, in connection with such merger or amalgamation, the then-outstanding shares
of Trenwick  Common Stock shall be changed into or exchanged  for stock or other
securities  of Trenwick or any other  person or cash or any other  property;  or
(iii) to sell or otherwise  transfer all or  substantially  all of its assets to
any person,  other than LaSalle or one of its  subsidiaries,  then,  and in each
such case, the agreement  governing such transaction shall make proper provision
so that  upon the  consummation  of such  transaction  and  upon the  subsequent
exercise of the Trenwick Option,  LaSalle shall be entitled to receive, for each
share of Trenwick Common Stock with respect to which the Trenwick Option has not
theretofore been exercised,  an amount of consideration in the form of and equal
to the per share amount of consideration that would be received by the holder of
one share of Trenwick  Common Stock (and, in the event of an election or similar
arrangement  with  respect to the type of  consideration  to be  received by the
holders of Trenwick  Common Stock,  subject to the foregoing,  proper  provision
shall be made so that the  holder of the  Trenwick  Option  would  have the same
election  or  similar  rights  as would the  holder  of the  number of shares of
Trenwick Common Stock for which the Trenwick Option is then exercisable).

                  10. Restrictive Legends. Each certificate  representing shares
of  Trenwick  Common  Stock  issued to LaSalle  at a Closing  will have typed or
printed thereon a restrictive legend in substantially the following form:

         THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
         UNDER THE SECURITIES  ACT OF 1933, AS AMENDED,  AND MAY BE REOFFERED OR
         SOLD ONLY IF SO  REGISTERED OR IF AN EXEMPTION  FROM SUCH  REGISTRATION
         IS  AVAILABLE.  SUCH   SECURITIES  ARE  ALSO   SUBJECT  TO   ADDITIONAL
         RESTRICTIONS  ON TRANSFER AS SET FORTH IN THE STOCK  OPTION  AGREEMENT,
         DATED  AS OF  DECEMBER  19,  1999,  A COPY OF  WHICH  MAY  BE  OBTAINED
         FROM THE ISSUER UPON REQUEST.

                  It is  understood  and agreed that:  (i) the  reference to the
resale  restrictions  of the Securities Act in the above legend shall be removed
by delivery of substitute  certificate(s)  without such reference if such Option
Shares have been  registered  pursuant to the Securities Act, such Option Shares
have  been  sold in  reliance  on and in  accordance  with  Rule 144  under  the
Securities  Act or LaSalle has delivered to Trenwick a copy of a letter from the
staff of the Securities and Exchange  Commission,  or an opinion of counsel,  in
form and substance  satisfactory to Trenwick and its counsel, to the effect that
such  legend is not  required  for  purposes  of the  Securities  Act;  (ii) the
reference to  restrictions  pursuant to this Agreement in the above legend shall
be removed by delivery of substitute  certificate(s)  without such  reference if
the Option Shares  evidenced by  certificate(s)  containing  such reference have
been sold or transferred in compliance with the provisions of this Agreement and
under  circumstances  that do not require the retention of such  reference;  and
(iii) the legend  shall be  removed in its  entirety  if the  conditions  in the
preceding  clauses  (i)  and  (ii)  are  both  satisfied.   In  addition,   such
certificate(s)  shall  bear  any  other  legend  as  may  be  required  by  law.
Certificates  representing  shares sold in a registered public offering pursuant
to Section 8 shall not be required to bear the legend set forth in this  Section
10.


                                       9



                  11.  Profit Limitation.

                  (a)  Notwithstanding  any other provision of this Agreement or
the Business Combination Agreement, in no event shall LaSalle's Total Profit (as
hereinafter  defined) exceed $15 million (such amount,  the "Profit Limit") and,
if it would otherwise exceed such amount, LaSalle, at its sole election,  shall,
within five  business  days,  either (i) deliver to the Issuer for  cancellation
Option Shares (valued,  for purposes of this Section 11, at their closing market
price on the NYSE on the date of such delivery),  (ii) pay cash to the Issuer or
refund in cash any Trenwick Termination Fee previously paid to LaSalle or reduce
or waive the amount of any Trenwick  Termination Fee payable to LaSalle pursuant
to Section 7.4(b) of the Business Combination Agreement,  or (iii) undertake any
combination  thereof, so that LaSalle's Total Profit shall not exceed the Profit
Limit after taking into account the foregoing  actions.  As used herein,  "Total
Profit" means the aggregate amount (before taxes) of (i) $12 million, payable in
excess of  expenses,  pursuant  to Section  7.4(c) of the  Business  Combination
Agreement,  (ii)  amounts  paid by Trenwick  pursuant to Section 12 hereof,  and
(iii) (x) the net cash amounts received by LaSalle pursuant to the sale or other
disposition  of Option  Shares (or any other  securities  into which such Option
Shares are converted or exchanged) to any unaffiliated party, less (y) LaSalle's
purchase price for such Option Shares.

                  (b)  Notwithstanding  any other provision of this Agreement or
the Business Combination Agreement, the Trenwick Option may not be exercised for
a number of Option  Shares that would,  as of the date of the  Exercise  Notice,
result in a Notional  Total  Profit (as  hereinafter  defined)  of more than the
Profit Limit and, if exercise of the Trenwick Option  otherwise would exceed the
Profit Limit,  LaSalle,  at its discretion,  may increase the Exercise Price for
that  number  of Option  Shares  set  forth in the  Exercise  Notice so that the
Notional Total Profit shall not exceed the Profit Limit; provided,  that nothing
in this sentence  shall restrict any exercise of the Trenwick  Option  permitted
hereby on any  subsequent  date at the  Exercise  Price  set forth in  Section 1
hereof.  As used herein,  the term  "Notional  Total Profit" with respect to any
number of Option Shares as to which LaSalle may propose to exercise the Trenwick
Option  shall be the  Total  Profit  determined  as of the date of the  Exercise
Notice  assuming that the Trenwick  Option were  exercised on such date for such
number of Option Shares and assuming that such Option Shares,  together with all
other shares of Trenwick Common Stock held by LaSalle and its subsidiaries as of
such  date,  were sold for cash at the  closing  market  price for the  Trenwick
Common  Stock  on the  NYSE  Composite  Tape at the  close  of  business  on the
preceding trading day (less customary brokerage commissions).



                                       10




                  12. Certain Repurchases.

                  (a) LaSalle  "Put".  Subject to the  limitations  set forth in
Section  11,  upon  delivery  of written  notice to  Trenwick  by  LaSalle  (the
"Repurchase Notice"):

                  (i)  at  any  time  during  which  the   Trenwick   Option  is
         exercisable pursuant to Section 2 (the "Repurchase  Period"),  Trenwick
         and its successors in interest shall repurchase from LaSalle all or any
         portion of the Trenwick Option, as specified by LaSalle,  at the Option
         Repurchase Price set forth in Section 12(b)(i); and

                  (ii) at any time  prior to the fifth  anniversary  of the date
         hereof,  Trenwick and its successors in interest shall  repurchase from
         LaSalle all or any portion of the Trenwick  Common  Stock  purchased by
         LaSalle  pursuant to the Trenwick Option,  as specified by LaSalle,  at
         the Share Repurchase Price set forth in Section 12(b)(iii).

                  (b)    Certain Definitions.   For purposes of this Section 12,
the following definitions shall apply:

                  (i) "Option  Repurchase  Price" shall mean (A) the  difference
         between the Option Repurchase Market/Offer Price (as defined below) for
         the Trenwick  Common Stock as of the date of the applicable  Repurchase
         Notice and the Exercise  Price,  multiplied by (B) the number of shares
         of Trenwick Common Stock purchasable pursuant to the Trenwick Option or
         the portion thereof covered by the applicable  Repurchase  Notice,  but
         only if the Option  Repurchase  Market/Offer  Price is greater than the
         Exercise Price.

                  (ii) "Option Repurchase  Market/Offer Price" shall mean, as of
         any date,  the higher of (X) the highest  price per share offered as of
         such date pursuant to any tender or exchange  offer or other offer with
         respect to a business  combination  offer involving  Trenwick or any of
         its material  subsidiaries  as the target party which was made prior to
         such date and not  terminated  or withdrawn as of such date and (Y) the
         Fair Market  Value (as  defined in Section  12(b)(v))  of the  Trenwick
         Common Stock as of such date.



                                       11



                  (iii) "Share  Repurchase  Price" shall mean the product of (A)
         the sum of (I) the Exercise Price paid by LaSalle per share of Trenwick
         Common Stock acquired  pursuant to the Trenwick  Option and (II) if the
         Share Repurchase  Market/Offer Price (as defined below) is greater than
         the  Exercise  Price,  the  difference  between  the  Share  Repurchase
         Market/Offer  Price  and the  Exercise  Price,  and (B) the  number  of
         Trenwick Common Stock to be repurchased pursuant to this Section 12.

                  (iv) "Share Repurchase  Market/Offer  Price" shall mean, as of
         any date,  the  higher  of (X) the  highest  price  per  share  offered
         pursuant to a tender or exchange  offer or other  business  combination
         offer  involving  Trenwick as the target  party  during the  Repurchase
         Period prior to the delivery by LaSalle of a notice of  repurchase  and
         (Y) the Fair Market Value of the Trenwick Common Stock as of such date.

                  (v) "Fair  Market  Value"  shall  mean,  with  respect  to any
         security, the per share average of the last sale prices on the NYSE (or
         such other national  stock exchange or national  market system as shall
         then be the primary  trading market for such security) for the ten (10)
         trading days immediately preceding the applicable date.

                  (c) Payment  and  Redelivery  of Trenwick  Options or Trenwick
         Common Stock. In the event that LaSalle exercises its rights under this
         Section 12, Trenwick shall,  within ten (10) business days  thereafter,
         pay the required  amount to LaSalle in immediately  available funds and
         LaSalle  shall  surrender  to  Trenwick  the  Trenwick  Option  or  the
         certificate  or  certificates  evidencing  the  Trenwick  Common  Stock
         purchased by LaSalle pursuant hereto, and LaSalle shall warrant that it
         has sole  beneficial  ownership of the Trenwick Option or such Trenwick
         Common Stock and that the Trenwick Option or such Trenwick Common Stock
         are then free and clear of all claims, liens, charges, encumbrances and
         security interests of any nature whatsoever.

                  (d)  Repurchase  Price  Reduced at  LaSalle's  Option. In
         the event that  payment of the  repurchase  price  specified in Section
         12(a)  would  subject  the  repurchase  of the  Trenwick  Option or the
         Trenwick  Common Stock  purchased  by LaSalle  pursuant to the Trenwick
         Option to a vote of the stockholders of Trenwick pursuant to applicable
         law, regulations,  or requirements of a national securities exchange or
         national  market system or the Trenwick  By-Laws,  then LaSalle may, at
         its  election,  reduce  the  repurchase  price or the  number of shares
         covered by the  LaSalle  repurchase  request to an amount  which  would
         permit such repurchase without the necessity for such a vote.

                  (e)      Repurchase at the Election of Trenwick.



                                       12



                  (i) Except to the extent that  LaSalle  shall have  previously
         exercised its rights under  Section  12(a),  at the written  request of
         Trenwick  during  the  six-month  period   immediately   following  the
         Repurchase  Period,  Trenwick may repurchase from LaSalle,  and LaSalle
         shall  sell to  Trenwick,  all (but not less than all) of the  Trenwick
         Common Stock  acquired by LaSalle  pursuant  hereto and with respect to
         which LaSalle has beneficial  ownership at the time of such repurchase,
         at a price  equal to the sum of (A) the  greater of (I) one hundred ten
         percent  (110%) of the  Current  Market  Price (as  defined  in Section
         12(e)(iii)) or (II) the sum of (X) the Purchase Price in respect of the
         shares so acquired plus (Y) LaSalle's Pre-Tax Carrying Cost (as defined
         in  Section  12(e)(iii)),  multiplied  in either  case by the number of
         shares so acquired, and (B) the amount of the documented  out-of-pocket
         expenses (to the extent not previously  reimbursed or  compensated  for
         pursuant  hereto or pursuant  to the  Business  Combination  Agreement)
         incurred  by  LaSalle  in  connection  with  the  Business  Combination
         Agreement and this Agreement and the transactions  contemplated thereby
         and hereby,  including  reasonable  accounting,  investment banking and
         legal fees (the "Section 12(e)  Repurchase  Consideration");  provided,
         that  Trenwick's  rights  under this  Section  12(e) shall be suspended
         (with any such rights  being  extended  accordingly)  during any period
         when the exercise of such rights would subject  LaSalle to liability or
         disgorgement of profits pursuant to Section 16(b) of the Exchange Act.

                  (ii) If  Trenwick  exercises  its rights  under  this  Section
         12(e),  Trenwick  shall,  within ten (10) business days pay the Section
         12(e)  Repurchase  Consideration  in  immediately  available  funds and
         LaSalle  shall  surrender  to  Trenwick  certificates   evidencing  the
         Trenwick Common Stock purchased hereunder with respect to which LaSalle
         then has  beneficial  ownership,  and LaSalle shall warrant that it has
         sole  beneficial  ownership of such Trenwick  Common Stock and that all
         such  shares  are then free and clear of all  claims,  liens,  charges,
         encumbrances and security interests of any nature whatsoever.

                  (iii) As used in Section 12(e)(i),  (A) "Current Market Price"
         shall mean the  average of the last sale  prices per share of  Trenwick
         Common  Stock on the NYSE for the ten  (10)  trading  days  immediately
         preceding the date of  Trenwick's  request for  repurchase  pursuant to
         this Section 12(e) and (B) "Pre-Tax Carrying Cost" shall mean an amount
         equal to the interest on the aggregate  purchase  price paid by LaSalle
         for the Trenwick Common Stock purchased pursuant to the Trenwick Option
         from the date of  purchase  to the  date of  repurchase  at the rate of
         interest  announced by  Citibank,  N.A. at its prime or base lending or
         reference rate during such period,  less any dividends  received on the
         shares so purchased, divided by the number of shares of Trenwick Common
         Stock so purchased.

                  13.   Binding   Effect;   No   Assignment;   No  Third   Party
Beneficiaries.  This Agreement shall be binding upon and inure to the benefit of
the  parties  hereto and their  respective  successors  and  permitted  assigns.
Neither this Agreement nor the rights or the  obligations of either party hereto
are  assignable,  except by operation of law, or with the written consent of the
other  party (it being  agreed  that all  transactions  contemplated  by Section
2.1(b) and (c) of the Business  Combination  Agreement  shall not be  considered
assignments  in  violation  of  this  Section  13).  Nothing  contained  in this
Agreement,  express or implied, is intended to confer upon any person other than
the parties hereto and their respective permitted assigns any rights or remedies
of any nature whatsoever by reason of this Agreement. Any Restricted Shares sold
by a  party  in  compliance  with  the  provisions  of  Section  8  shall,  upon
consummation of such sale, be free of the  restrictions  imposed with respect to
such shares by this Agreement,  unless and until such party shall  repurchase or
otherwise become the beneficial owner of such shares, and any transferee of such
shares shall not be entitled to the registration rights of such party.



                                       13




                  14. Specific Performance. The parties recognize and agree that
if for any reason any of the  provisions of this  Agreement are not performed in
accordance  with their specific terms or are otherwise  breached,  immediate and
irreparable  harm or injury would be caused for which money damages would not be
an adequate  remedy.  Accordingly,  each party agrees that, in addition to other
remedies,  the other party shall be entitled to an  injunction  restraining  any
violation or threatened  violation of the provisions of this  Agreement.  In the
event that any action  should be brought in equity to enforce the  provisions of
the  Agreement,  neither  party will allege,  and each party  hereby  waives the
defense, that there is adequate remedy at law.

                  15. Entire Agreement. This Agreement, the Business Combination
Agreement (including any exhibits and schedules thereto) and the Confidentiality
Agreement  constitute  the  entire  agreement,  and  supersede  all other  prior
agreements and  understandings,  both written and oral, between the parties with
respect to the subject matter of this Agreement.

                  16.  Further  Assurances.  Each party will execute and deliver
all such further  documents and  instruments and take all such further action as
may be necessary in order to consummate the transactions contemplated hereby.

                  17.  Validity.  The  invalidity  or  unenforceability  of  any
provision of this Agreement shall not affect the validity or  enforceability  of
the other  provisions  of this  Agreement,  which shall remain in full force and
effect. In the event any court or other competent authority holds any provisions
of this Agreement to be null,  void or  unenforceable,  the parties hereto shall
negotiate  in good faith the  execution  and  delivery of an  amendment  to this
Agreement  in  order,  as nearly  as  possible,  to  effectuate,  to the  extent
permitted  by law,  the  intent  of the  parties  hereto  with  respect  to such
provision and the economic effects thereof.  If for any reason any such court or
regulatory  agency  determines that LaSalle is not permitted to acquire the full
number of shares of Trenwick  Common Stock  provided in Section 1 hereof (as the
same may be adjusted),  it is the express intention of Trenwick to allow LaSalle
to acquire  such  lesser  number of shares as may be  permissible,  without  any
amendment or modification  hereof.  Each party agrees that,  should any court or
other competent authority hold any provision of this Agreement or part hereof to
be  null,  void  or  unenforceable,  or  order  any  party  to take  any  action
inconsistent  herewith,  or not take any action required herein, the other party
shall not be entitled to specific  performance  of such provision or part hereof
or to any other remedy,  including but not limited to money damages,  for breach
hereof or of any other  provision of this Agreement or part hereof as the result
of such holding or order.


                                       14




                  18. Notices. All notices,  requests, claims, demands and other
communications  under this  Agreement  shall be in  writing  and shall be deemed
given if (i) delivered,  personally,  or (ii) sent by overnight  courier service
(providing proof of delivery), or (iii) telecopied (which is confirmed), or (iv)
five (5) days after being mailed by registered or certified mail (return receipt
requested) to the parties at the  following  addresses (or at such other address
for a party as shall be specified by like notice):

                  If to Trenwick:

                           Alan L. Hunte
                           Vice President and
                              Chief Financial Officer
                           Trenwick Group Inc.
                           One Canterbury Green
                           Stamford, CT 06901
                           Fax: (203) 353-5550

                  with a copy to:

                           Baker & McKenzie
                           805 Third Avenue
                           New York, New York 10022
                           Attention: James R. Cameron
                           Fax: (212) 891-3835

                  If to LaSalle, to:

                           LaSalle Re Holdings Limited
                           Continental Building
                           25 Church Street
                           Hamilton HM 12
                           Bermuda
                           Fax: (441) 292-1501

                  with a copy to:

                           Mayer, Brown & Platt
                           190 S. LaSalle Street
                           Chicago, Illinois 60603
                           Attention: Richard W. Shepro
                           Fax: (312) 701-7711




                                       15



                  19.  Governing Law;  Choice of Forum.  This Agreement shall be
governed by, and construed in accordance with, the laws of the State of Delaware
without regard to the conflicts of law principles  thereof.  Each of the parties
hereto (a) consents to submit itself to the personal jurisdiction of any federal
court located in the State of Delaware or any Delaware  state court in the event
any dispute arises out of this Agreement or any of the transactions contemplated
by this  Agreement,  (b) agrees  that it will not attempt to deny or defeat such
personal  jurisdiction  by motion or other request for leave from any such court
and (c) agrees that it will not bring any action  relating to this  Agreement or
any of the transactions contemplated by this Agreement in any court other than a
federal court sitting in the state of Delaware or a Delaware state court.

                  20. Interpretation. When a reference is made in this Agreement
to a Section,  such  reference  shall be to a Section of this  Agreement  unless
otherwise indicated. Whenever the words "include", "includes" or "including" are
used in this  Agreement,  they  shall be  deemed  to be  followed  by the  words
"without   limitation."  The  descriptive   headings  herein  are  inserted  for
convenience  of  reference  only and are not intended to be part of or to affect
the meaning or interpretation of this Agreement.

                  21.  Counterparts.  This  Agreement  may be executed in one or
more counterparts,  each of which shall be deemed to be an original, but both of
which, taken together, shall constitute one and the same instrument.

                  22. Expenses. Except as otherwise expressly provided herein or
in the  Business  Combination  Agreement,  all costs and  expenses  incurred  in
connection with the transactions contemplated by this Agreement shall be paid by
the party incurring such expenses.

                  23. Amendment. This Agreement may not be amended, except by an
instrument in writing signed on behalf of each of the parties.

                  24. Waiver.  Any agreement on the part of a party to waive any
provision  of this  Agreement,  or to extend the time for  performance,  will be
valid only if set forth in an  instrument  in  writing  signed on behalf of such
party.  The failure of any party to this  Agreement  to assert any of its rights
under this Agreement or otherwise will not constitute a waiver of such rights.




                                       16




                  25. Loss or  Mutilation.  Upon receipt by Trenwick of evidence
reasonably  satisfactory to it of the loss, theft,  destruction or mutilation of
this  Agreement,  and (in the case of loss,  theft or destruction) of reasonably
satisfactory  indemnification,  and  upon  surrender  and  cancellation  of this
Agreement,  if  mutilated,  Trenwick  will  execute and deliver to LaSalle a new
Agreement of like tenor and date. Any such new Agreement  executed and delivered
will  constitute an additional  contractual  obligation on the part of Trenwick,
whether or not the Agreement so lost, stolen,  destroyed,  or mutilated shall at
any time be enforceable by anyone.

                  26. Extension of Time Periods.  The time periods for exercises
of certain rights  hereunder shall be extended (but in no event by more than six
(6) months):  (a) to the extent necessary to obtain all  governmental  approvals
for the exercise of such rights, and for the expiration of all statutory waiting
periods;  and (b) to the extent necessary to avoid any liability or disgorgement
of profits under Section 16(b) of the Exchange Act by reason of such exercise.

                  27.  Further  Assurance.  Each  party  agrees to  execute  and
deliver all such further  documents  and  instruments  and take all such further
action as may be necessary in order to consummate the transactions  contemplated
hereby.











                                       17




                  IN WITNESS  WHEREOF,  the  parties  hereto  have  caused  this
Agreement to be executed by their respective duly authorized  officers as of the
date first above written.

                                    TRENWICK GROUP INC.


                                    By: /s/ James F. Billett, Jr.
                                        ----------------------------------
                                        Name:  James F. Billett, Jr.
                                        Title: Chairman, President and Chief
                                               Executive Officer


                                    LASALLE RE HOLDINGS LIMITED


                                    By: /s/ Guy D. Hengesbaugh
                                        ----------------------------------
                                        Name:  Guy D. Hengesbaugh
                                        Title: President and Chief Executive
                                               Officer