TRENWICK GROUP INC. AND LASALLE RE HOLDINGS LIMITED TO MERGE

      Stamford, Connecticut and Hamilton, Bermuda, December 19, 1999 . . .

Trenwick Group Inc.  ("Trenwick")  (NYSE:  TWK) and LaSalle Re Holdings  Limited
("LaSalle Re") (NYSE:  LSH)  announced  today that they have signed a definitive
agreement  for  Trenwick  and  LaSalle Re to merge,  with  shareholders  of both
companies receiving shares in a new Bermuda holding company to be named Trenwick
Group Ltd. James F. Billett, Jr. will continue as Chairman,  President and Chief
Executive  Officer of the new Trenwick,  and Guy D.  Hengesbaugh,  President and
Chief  Executive  Officer of LaSalle Re, will continue in those roles at LaSalle
Re, which will become a subsidiary of the new  Trenwick.  The Board of Directors
of the new Trenwick will consist of the twelve current Trenwick  directors,  and
four directors from the present LaSalle Re Board.

Under the terms of the merger agreement, shareholders of Trenwick and LaSalle Re
will each receive  shares in the newly formed  Trenwick on a one-for-one  basis.
The transaction is expected to be tax-free to shareholders of both companies.

James F.  Billett,  Jr.,  Trenwick's  Chairman,  President  and Chief  Executive
Officer,  said, "This strategic  merger creates a significant new  Bermuda-based
global  insurance  and  reinsurance  underwriting   organization  with  a  total
capitalization of over $1.2 billion. This transaction,  which is the most recent
step in Trenwick's  strategic  evolution,  is exciting for us since it creates a
company  with  larger  scale  and  stronger   competitive   capabilities   in  a
consolidating global  insurance/reinsurance  market, adds higher margin business
to Trenwick's  existing mix,  creates a better  platform to enhance  shareholder
returns,  and expands the management depth of Trenwick by adding Guy Hengesbaugh
and his team. The combined  enterprise  will have a strong presence in the three
most significant  insurance markets in the world: the United States,  London and
Bermuda."

"This merger represents a tremendous step forward in offering LaSalle Re clients
top-notch financial security while giving LaSalle Re shareholders the
opportunity to realize greater value," said Guy D. Hengesbaugh, President and
Chief Executive Officer of LaSalle Re.

On a combined basis, the new Trenwick would have had assets in excess of
$3.5 billion, shareholders' equity of over $950 million and total capitalization
of  approximately  $1.2  billion  as of  September  30,  1999.  Based on current
projections,  combined 1999 gross  written  premiums for all of the new Trenwick
companies are expected to approach $1.0 billion.

The companies  believe that the transaction  provides a cost-effective  means of
augmenting capital and adding structural  platforms for further  expansion.  The
addition of LaSalle Re's high margin specialist property catastrophe reinsurance
business continues Trenwick's strategy of entering new markets and product lines
that began with  Trenwick's  acquisition  of  Trenwick  International  (formerly
Sorema U.K.),  completed in February 1998, and Trenwick's recent  acquisition of
Chartwell Re Corporation,  completed in October 1999. The addition of LaSalle Re
will provide the new Trenwick with a significant level of financial  flexibility
and the  opportunity to develop new business  products.  Trenwick and LaSalle Re
expect that consolidating the two companies will generate significant  financial
benefits and will be accretive to Trenwick's and LaSalle Re's shareholders.

CNA  Financial  Corporation  and  Aon  Corporation,   founding  and  significant
shareholders of LaSalle Re, have each agreed to vote in favor of the merger.

Bernard L.  Hengesbaugh,  Chairman and Chief Executive Officer of CNA Insurance,
stated, "CNA wholeheartedly endorses the transaction, which is highly beneficial
for LaSalle Re's  shareholders and clients.  This transaction  further evidences
CNA's commitment to providing creative solutions, which are best met in a global
platform."


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Michael D.  O'Halleran,  President and Chief Operating  Officer of Aon,  stated,
"Aon is very pleased to support the merger of LaSalle Re with Trenwick.  We have
worked with Trenwick and its CEO, Jim Billett, for many years, and recognize the
outstanding opportunity this transaction provides for the combined companies and
their shareholders and clients."

The  transaction  is  subject  to  the  approval  of the  respective  companies'
shareholders,  regulatory approvals and other customary closing conditions.  The
transaction is expected to be completed early in the second quarter of 2000. The
merger  agreement  provides for the payment of  termination  fees under  certain
circumstances,  and Trenwick  and LaSalle Re have also  entered  into  customary
"cross" stock option agreements.

Trenwick  Group  Inc.  is  a  holding  company  with  four  principal  operating
subsidiaries: Trenwick America Re, which provides treaty reinsurance to insurers
of property and casualty  risks in the United  States;  Trenwick  International,
which  underwrites  treaty  and  facultative  reinsurance  as well as  specialty
insurance on a worldwide basis;  Chartwell  Managing Agents Limited,  Trenwick's
managing  agency  at  Lloyd's;   and  Canterbury  Financial  Group  Inc.,  which
underwrites  U.S.  property and casualty  insurance  through  specialty  program
administrators.   All  of  Trenwick's   principal   insurance  and   reinsurance
subsidiaries  are rated A  (Excellent)  by A.M.  Best Company and are assigned a
financial strength rating of A+ by Standard & Poor's.

LaSalle Re is a property and casualty  reinsurer  writing  worldwide  specialist
products  with an  emphasis  on  catastrophe  coverage.  LaSalle  Re is  rated A
(Excellent)  by A.M. Best Company and currently  holds an A- financial  strength
rating from Standard & Poor's.

Donaldson, Lufkin & Jenrette Securities Corporation acted as financial advisor
to Trenwick; Lazard Freres & Co. LLC, Salomon Smith Barney Inc. and Aon Capital
Markets, Inc. acted as financial advisors to LaSalle Re.

                                     * * *
This press release contains forward looking statements of management's beliefs,
estimates,  projections and assumptions for the financial condition,  results of
operations,  business and  prospects of Trenwick  after the  transaction.  These
forward looking statements  involve certain risks and  uncertainties,  including
those  detailed  from time to time in  Trenwick's  and LaSalle  Re's reports and
filings with the Securities and Exchange Commission. Additional factors that may
cause  actual  results  to differ  materially  from those  contemplated  by such
forward looking  statements  include,  among others,  that the completion of the
transaction  may be  delayed  or not  occur,  that  difficulties  related to the
integration  of the  businesses  of Trenwick  and  LaSalle Re are  greater  than
expected or that expectations for growth may not be realizable.

December 19, 1999


Contacts:                  Alan L. Hunte, Executive Vice President, and
                           Chief Financial Officer
                           Trenwick Group Inc. (NYSE: TWK)
                           (203) 353-5500

                           Diane Newman, Investor Relations Manager
                           LaSalle Re Holdings Limited (NYSE: LSH )
                           (441) 292-3339



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