TRENWICK STOCK OPTION AGREEMENT

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

                  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  Trenwick's  willingness  to enter
into the Business  Combination  Agreement,  Trenwick has requested  that LaSalle
agree, and LaSalle has so agreed,  to grant to Trenwick an option to purchase up
to 3,105,110  common  shares,  par value $1.00 per share,  of LaSalle  ("LaSalle
Common  Shares") in accordance  with the terms and subject to the conditions set
forth herein.

                  NOW, THEREFORE,  to induce Trenwick 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,  LaSalle  hereby  grants to Trenwick an  irrevocable  option (the
"LaSalle  Option") to purchase up to 3,105,110 (as adjusted as set forth herein)
shares (the  "Option  Shares") of LaSalle  Common  Shares (such number of Option
Shares representing 19.9% of the LaSalle Common Shares issued and outstanding on
the date hereof) in the manner set forth below at a price (the "Exercise Price")
of $12.81 per Option Share (which price per share is equal to the average of the
last  sale  prices  of  LaSalle  Common  Shares  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 LaSalle Option is exercisable exceed 19.9% of the number of
issued and outstanding shares of LaSalle Common Shares.

                  2.  Exercise of Option. The LaSalle Option may be exercised by
Trenwick,  in whole  or in part,  at any  time or from  time to time  after  the
Business   Combination   Agreement   becomes   terminable   by  Trenwick   under
circumstances  which  would or could  entitle  Trenwick  to receive  the LaSalle





Termination Fee pursuant to Section 7.4(c) 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 Trenwick wishes to exercise the LaSalle Option,  Trenwick shall deliver to
LaSalle a written notice (an "Exercise  Notice")  specifying the total number of
Option  Shares it wishes to purchase and 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 Trenwick  in an Exercise  Notice
delivered  at least  two (2)  business  days  prior  to the  date of the  Option
Closing.  The  LaSalle  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  LaSalle  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
LaSalle Option may not be exercised if Trenwick 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 Trenwick to LaSalle 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, Trenwick
shall be deemed to be the holder of record of the Option  Shares  issuable  upon
such  exercise,  notwithstanding  that the stock transfer books of LaSalle shall
then be closed or that  certificates  representing  such Option Shares shall not
then be actually delivered to Trenwick.

                  3.  Conditions to Closing.  The obligation of LaSalle to issue
the Option  Shares to Trenwick  hereunder  is subject to the  conditions,  which
(other than the  conditions  described in clauses (i), (iii) and (iv) below) may
be waived by LaSalle 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 Trenwick; 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, Trenwick  shall pay to LaSalle
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 LaSalle  Common  Shares  purchased  pursuant  to the  exercise of the LaSalle
Option  in  immediately  available  funds  by wire  transfer  to a bank  account
designated in writing by LaSalle; provided,  however, that failure or refusal of
LaSalle to designate  such account shall not preclude  Trenwick from  exercising
the  LaSalle  Option.  At  Trenwick's  option,  in lieu of  delivering  the cash
Exercise  Price,  Trenwick  may  instruct  LaSalle in writing to deduct from the
number of shares of LaSalle  Common  Shares that would  otherwise be issued upon
such exercise, a number of shares of LaSalle Common Shares equal to the quotient
obtained from dividing:

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

                  (y) the Fair Market Value of a share of LaSalle Common Shares.

"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), LaSalle will deliver
to Trenwick a certificate or certificates representing the number of Option
Shares to be purchased by Trenwick 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,  LaSalle  shall
deliver a new option  evidencing the rights of Trenwick  thereof to purchase the
balance of the shares  purchasable  hereunder  and (ii) Trenwick will deliver to
LaSalle a copy of this  Agreement  and a letter  agreeing that Trenwick will not
offer to sell or otherwise dispose of such shares in violation of applicable law
or the provisions of this Agreement. LaSalle 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  Trenwick  or its  designee.
LaSalle shall use its reasonable best efforts to cause the LaSalle Common Shares
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.

                  5.  Representations and Warranties of LaSalle.  LaSalle hereby
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,  (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


                                       3



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, 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,  (d)
LaSalle has taken all  necessary  corporate  action to authorize and reserve for
issuance and to permit it to issue, upon exercise of the LaSalle Option,  and at
all times from the date hereof through the expiration of the LaSalle Option will
have  reserved,  3,105,110  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  Trenwick  upon the  exercise  of the LaSalle  Option,  Trenwick  will
acquire  the  Option  Shares  free and  clear  of all  claims,  liens,  charges,
encumbrances  and  security  interests  of any  nature  whatsoever,  (f) none of
LaSalle,  any of its  affiliates  or anyone  acting on its or their  behalf  has
issued,   sold  or  offered  any   security  of  LaSalle  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 Trenwick  contained in Section 6(d) are true and correct and
based on Trenwick'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  LaSalle  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 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 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 LaSalle or
any of its subsidiaries,  pursuant to (i) any provision of the LaSalle Bye-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 LaSalle 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 LaSalle 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 LaSalle.

                  6.  Representations  and  Warranties  of  Trenwick.   Trenwick
represents  and  warrants to LaSalle  that (a)  Trenwick is a  corporation  duly



                                       4




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
and to carry out its  obligations  hereunder,  (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  and  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, and (d) any Option
Shares  acquired  upon  exercise  of the LaSalle  Option  will be  acquired  for
Trenwick's own account,  for  investment  purposes only and will not be, and the
LaSalle  Option is not being,  acquired  by  Trenwick  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 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 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
Trenwick  or any of its  subsidiaries,  pursuant  to (i)  any  provision  of the
certificate of incorporation or by-laws of Trenwick,  (ii) any 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 any of their  properties or assets are bound,  or (iii) any
judgment,  order, decree, statute, law, ordinance, rule or regulation applicable
to Trenwick,  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 Trenwick.

                  7.   Restrictions on Transfer.

                  (a)  Restrictions on Transfer.  Prior to the first anniversary
of the date on  which  Trenwick  purchases  any  Option  Shares  hereunder  (the
"Expiration Date"), Trenwick 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 Trenwick  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,  Trenwick  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.

                  (b) Permitted Sales. Following the termination of the Business
Combination  Agreement,  Trenwick  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 LaSalle,  by a majority of the members of the Board of  Directors  of LaSalle
(which  majority shall include a majority of directors who were directors  prior
to the announcement of such tender or exchange offer or merger).




                                       5




                  (c)  LaSalle'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 LaSalle Common Shares
pursuant  to the  LaSalle  Option,  if Trenwick  shall  desire to sell,  assign,
transfer or otherwise  dispose of any shares of LaSalle  Common  Shares or other
securities  acquired by it pursuant to the LaSalle  Option,  Trenwick shall give
LaSalle written notice of the proposed  transaction (a "Trenwick Offer Notice"),
identifying the proposed transferee, accompanied by a copy of a binding offer to
purchase  such  LaSalle  Common  Shares  or  other  securities  signed  by  such
transferee and setting forth the terms of the proposed  transaction.  A Trenwick
Offer  Notice  shall be deemed an offer by Trenwick  to  LaSalle,  which must be
accepted,  if at all,  within  five (5)  business  days of the  receipt  of such
Trenwick Offer Notice, on the same terms and conditions and at the same price at
which  Trenwick is proposing to transfer  such  LaSalle  Common  Shares or other
securities  to such  transferee.  The purchase of any LaSalle  Common  Shares or
other  securities by LaSalle  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
Trenwick in immediately  available funds. In the event of the failure or refusal
of LaSalle to purchase  all of the  LaSalle  Common  Shares or other  securities
covered by a Trenwick  Offer  Notice,  Trenwick  may sell all, but not less than
all,  of  such  LaSalle  Common  Shares  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 Trenwick Offer Notice;
provided  that the  provisions  of this  sentence  shall not  limit  the  rights
Trenwick  may  otherwise  have in the  event  LaSalle  has  accepted  the  offer
contained in the Trenwick  Offer Notice and  wrongfully  refuses to purchase the
LaSalle Common Shares 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 LaSalle,  (ii) any  disposition  of LaSalle
Common Shares or other  securities by a person to whom Trenwick has assigned its
rights under the LaSalle  Option with the consent of LaSalle,  (iii) any sale by
means of a public  offering  registered  under the  Securities  Act, or (iv) any
transfer to a wholly-owned  subsidiary of Trenwick which agrees in writing to be
bound by the terms hereof.

                  8.   Registration  Rights.  Following the  termination  of the
Business Combination Agreement, but not later than the second anniversary of the
last date that Trenwick  acquired Option Shares under this  Agreement,  Trenwick
may by written notice (the "Registration  Notice") to LaSalle request LaSalle to
register  under  the  Securities  Act all or any part of the  Restricted  Shares
beneficially owned by Trenwick (the  "Registrable  Securities") pursuant  to   a
bona fide firm commitment underwritten public offering in which Trenwick and the
underwriters shall effect as wide a distribution of such Registrable  Securities
as is reasonably practicable and shall use their commercially reasonable efforts




                                       6



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  LaSalle  on a fully  diluted  basis (a  "Permitted
Offering").  The  Registration  Notice shall include a  certificate  executed by
Trenwick 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.  LaSalle  (and/or any
person  designated by LaSalle) shall  thereupon  have the option  exercisable by
written  notice  delivered to Trenwick  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 LaSalle and (ii) the then Fair Market Value of
such shares.  Any such  purchase of  Registrable  Securities  by LaSalle (or its
designee)  hereunder  shall take place at a closing to be held at the  principal
executive  offices of LaSalle or at the offices of its counsel at any reasonable
date and time  designated by LaSalle  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 LaSalle 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)  Trenwick  shall  not be
entitled to more than an  aggregate  of two  effective  registration  statements
hereunder  and (ii) LaSalle  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)  LaSalle 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
LaSalle, such information would have to be disclosed if a registration statement
were filed at that time;  (B) LaSalle is required  under the  Securities  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)  LaSalle  determines,  in its  reasonable
judgment, that such registration would interfere with any financing, acquisition
or  other  material  transaction  involving  LaSalle  or any of its  affiliates.
LaSalle  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 Trenwick may reasonably
request and shall continue such  registration or qualification in effect in such
jurisdiction;  provided,  however, that LaSalle 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.



                                       7




                  The  registration  rights  set  forth  in this  Section  8 are
subject  to  the  condition  that  Trenwick  shall  provide  LaSalle  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 LaSalle,  is necessary to enable
LaSalle 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 LaSalle's expense,  except for underwriting discounts and commissions and the
fees and the expenses of counsel to Trenwick,  and LaSalle  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 Trenwick shall
only be required to indemnify other parties to such  underwriting  agreement for
information  relating to such  Trenwick 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).

                  LaSalle   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 LaSalle  contained in this Agreement or in the
Business  Combination  Agreement,  in the event of any change in LaSalle  Common
Shares  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 LaSalle
Option,  and the Exercise Price per Option Share provided in Section 1, shall be
adjusted  appropriately to restore to Trenwick its rights  hereunder,  including
the right to purchase  from the LaSalle  (or its  successors)  shares of LaSalle
Common Shares  representing  19.9% of the outstanding  LaSalle Common Shares for
the aggregate  Exercise  Price  calculated  as of the date of this  Agreement as
provided in Section 1.


                                       8




                  (b) In the event that LaSalle  shall enter into an  agreement:
(i) to consolidate with merge or amalgamate into any person, other than Trenwick
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 Trenwick or one of its subsidiaries,  to merge or amalgamate
into LaSalle and LaSalle shall be the continuing or surviving corporation,  but,
in connection with such merger or amalgamation,  the then-outstanding  shares of
LaSalle  Common  Shares shall be changed  into or  exchanged  for stock or other
securities  of LaSalle  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 Trenwick 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 LaSalle Option,  Trenwick shall be entitled to receive, for each
share of LaSalle  Common Shares with respect to which the LaSalle 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 LaSalle  Common Shares (and, in the event of an election or similar
arrangement  with  respect to the type of  consideration  to be  received by the
holders of LaSalle Common Shares,  subject to the  foregoing,  proper  provision
shall be made so that the  holder  of the  LaSalle  Option  would  have the same
election  or  similar  rights  as would the  holder  of the  number of shares of
LaSalle Common Shares for which the LaSalle Option is then exercisable).



                  10. Restrictive Legends. Each certificate  representing shares
of LaSalle  Common  Shares  issued to Trenwick  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 Trenwick has delivered to LaSalle 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 LaSalle 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 Trenwick's Total Profit
(as hereinafter  defined)  exceed $15 million (such amount,  the "Profit Limit")
and, if it would otherwise exceed such amount,  Trenwick,  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  LaSalle  Termination  Fee  previously  paid to
Trenwick or reduce or waive the amount of any LaSalle Termination Fee payable to
Trenwick pursuant to Section 7.4(c) of the Business  Combination  Agreement,  or
(iii) undertake any combination  thereof,  so that Trenwick'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 LaSalle pursuant to Section
12 hereof and (iii) (x) the net cash  amounts  received by Trenwick  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) Trenwick's purchase price for such Option Shares.

                  (b)  Notwithstanding  any other provision of this Agreement or
the Business Combination Agreement,  the LaSalle 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 LaSalle Option  otherwise  would exceed the
Profit Limit,  Trenwick, 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 LaSalle  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 Trenwick may propose to exercise the LaSalle
Option  shall be the  Total  Profit  determined  as of the date of the  Exercise
Notice  assuming  that the LaSalle  Option were  exercised on such date for such
number of Option Shares and assuming that such Option Shares,  together with all
other shares of LaSalle Common Shares held by Trenwick and its  subsidiaries  as
of such date,  were sold for cash at the  closing  market  price for the LaSalle
Common  Shares  on the  NYSE  Composite  Tape at the  close of  business  on the
preceding trading day (less customary brokerage commissions).




                                       10



                  12. Certain Repurchases.

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

                  (i) at any time during which the LaSalle Option is exercisable
         pursuant  to  Section  2 (the  "Repurchase  Period"),  LaSalle  and its
         successors  in  interest  shall  repurchase  from  Trenwick  all or any
         portion of the LaSalle Option, as specified by Trenwick,  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,  LaSalle and its successors in interest shall  repurchase  from
         Trenwick all or any portion of the LaSalle  Common Shares  purchased by
         Trenwick pursuant to the LaSalle Option,  as specified by Trenwick,  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 LaSalle Common Shares as of the date of the  applicable  Repurchase
         Notice and the Exercise  Price,  multiplied by (B) the number of shares
         of LaSalle Common Shares purchasable  pursuant to the LaSalle 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 LaSalle 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 LaSalle  Common
         Shares as of such date.

                  (iii) "Share  Repurchase  Price" shall mean the product of (A)
         the sum of (I) the Exercise Price paid by Trenwick per share of LaSalle
         Common Shares  acquired  pursuant to the LaSalle 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
         LaSalle Common Shares to be repurchased pursuant to this Section 12.




                                       11



                  (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  LaSalle as the  target  party  during the  Repurchase
         Period prior to the delivery by Trenwick of a notice of repurchase  and
         (Y) the Fair Market Value of the LaSalle Common Shares 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  LaSalle  Options or LaSalle
Common  Shares.  In the event that  Trenwick  exercises  its  rights  under this
Section 12, LaSalle  shall,  within ten (10) business days  thereafter,  pay the
required  amount to Trenwick in immediately  available  funds and Trenwick shall
surrender  to LaSalle  the LaSalle  Option or the  certificate  or  certificates
evidencing the LaSalle Common Shares purchased by Trenwick pursuant hereto,  and
Trenwick  shall  warrant  that it has sole  beneficial  ownership of the LaSalle
Option or such LaSalle Common Shares and that the LaSalle Option or such LaSalle
Common  Shares  are  then  free  and  clear  of  all  claims,   liens,  charges,
encumbrances and security interests of any nature whatsoever.

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

                  (e) Repurchase at the Election of LaSalle.

                  (i) Except to the extent that Trenwick  shall have  previously
         exercised its rights under  Section  12(a),  at the written  request of
         LaSalle  during  the  six-month   period   immediately   following  the
         Repurchase Period,  LaSalle may repurchase from Trenwick,  and Trenwick
         shall  sell to  LaSalle,  all (but not less  than  all) of the  LaSalle
         Common Shares acquired by Trenwick  pursuant hereto and with respect to
         which Trenwick 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)  Trenwick'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  Trenwick  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  LaSalle'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  Trenwick to liability or disgorgement  of profits  pursuant to
         Section 16(b) of the Exchange Act.



                                       12




                  (ii) If LaSalle exercises its rights under this Section 12(e),
         LaSalle  shall,  within ten (10)  business  days pay the Section  12(e)
         Repurchase  Consideration  in immediately  available funds and Trenwick
         shall surrender to LaSalle  certificates  evidencing the LaSalle Common
         Shares  purchased  hereunder  with respect to which  Trenwick  then has
         beneficial  ownership,  and  Trenwick  shall  warrant  that it has sole
         beneficial  ownership of such LaSalle  Common  Shares 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 LaSalle
         Common  Shares on the NYSE for the ten (10)  trading  days  immediately
         preceding the date of LaSalle'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 Trenwick
         for the LaSalle Common Shares purchased  pursuant to the LaSalle 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 LaSalle Common
         Shares 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 Trenwick is not permitted to acquire the full
number of shares of LaSalle  Common Shares  provided in Section 1 hereof (as the
same may be adjusted),  it is the express intention of LaSalle to allow Trenwick
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.

                  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):



                                       14




                  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

                  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.



                                       15




                  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.

                  25. Loss or  Mutilation.  Upon  receipt by LaSalle 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,  LaSalle  will  execute and deliver to Trenwick 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 LaSalle,
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.




                                       16



                  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







                                       18