<PAGE>

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


                                                                   EXHIBIT 2.5





                            AGREEMENT AND PLAN OF MERGER

                      DATED AS OF THE 10th DAY OF OCTOBER 1997

                                   BY AND BETWEEN

                              SOUTHERN CALIFORNIA BANK

                                        AND

                        NATIONAL BANK OF SOUTHERN CALIFORNIA







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



<PAGE>


          AGREEMENT AND PLAN OF MERGER, dated as of the tenth day of October, 
1997 (this "Plan"), by and between Southern California Bank, a California 
banking corporation ("SC Bank"), and National Bank of Southern California, a 
national banking association ("NBSC").


                                      RECITALS:

          A.  SC BANK.  SC Bank is a banking corporation duly incorporated, 
validly existing and in good standing under the laws of the State of 
California, with its principal executive offices located in Anaheim, 
California.  As of the date hereof, SC Bank has (i) 1,028,286 authorized 
shares of common stock, no par value ("SC Bank Common Stock"), of which no 
more than 493,759 shares were outstanding as of the date hereof and (ii) no 
other class of capital stock authorized.  All of the outstanding shares of 
capital stock of SC Bank are owned by Western Bancorp, a California 
corporation ("Western").

          B.  SC BANK RIGHTS, ETC.  SC Bank does not have any shares of its 
capital stock reserved for issuance, any outstanding option, call or 
commitment relating to shares of its capital stock or any outstanding 
securities, obligations or agreements convertible into or exchangeable for, 
or giving any individual, corporation, partnership, association, trust or 
unincorporated organization (hereinafter "Person") any right (including, 
without limitation, preemptive rights) to subscribe for or acquire from it, 
any shares of its capital stock.

          C.  NBSC.  NBSC is a national banking association duly 
incorporated, validly existing and in good standing under the laws of the 
United States of America, with its principal executive offices located in 
Newport Beach, California.  As of the date hereof, NBSC has (i) 562,500 
authorized shares of common stock, $5.00 par value ("NBSC Common Stock"), of 
which no more than 450,000 shares were outstanding as of the date hereof and 
(ii) no other class of capital stock authorized.  All of the outstanding 
shares of capital stock of NBSC are owned by Western.

          D.  NBSC RIGHTS, ETC.  NBSC does not have any shares of its capital 
stock reserved for issuance, any outstanding option, call or commitment 
relating to shares of its capital stock or any outstanding securities, 
obligations or agreements convertible into or exchangeable for, or giving any 
Person any right (including, without limitation, preemptive rights) to 
subscribe for or acquire from it, any shares of its capital stock.



<PAGE>

          E.  APPROVALS. The respective Boards of Directors of SC Bank and 
NBSC have, or will have prior to the Effective Time (as defined in Section 
6.1 hereof), duly approved this Plan and have, or will have prior to the 
Effective Time, duly authorized its execution and delivery, and the sole 
shareholder of SC Bank and the sole shareholder of NBSC have, or will have 
prior to the Effective Time, approved the terms of this Plan.  Accordingly, 
no dissenters' rights will be exercised by the sole shareholder of either SC 
Bank or NBSC.

          In consideration of their mutual promises and obligations 
hereunder, the parties hereto adopt and make this Plan and prescribe the 
terms and conditions hereof and the manner and basis of carrying it into 
effect, which shall be as follows:


                           ARTICLE I.  THE MERGER

          SECTION 1.1.  STRUCTURE OF THE MERGER.  On the Effective Date (as 
defined in Section 6.1 hereof), NBSC will merge (the "Merger") with and into 
SC Bank, with SC Bank being the surviving corporation (the "Surviving 
Corporation"), pursuant to the provisions of, and with the effect provided 
in, the California Financial Code and the California General Corporation Law 
(the "Banking Law").  The corporate existence of SC Bank and NBSC shall be 
merged into and continued in the Surviving Corporation and the Surviving 
Corporation shall be deemed to be the same corporation as SC Bank and NBSC.  
All rights, franchises, and interests of SC Bank and NBSC in and to every 
type of property (real, personal or mixed) and choses in action shall be 
transferred to and vested in the Surviving Corporation by virtue of the 
Merger and without any deed or other transfer.  The Surviving Corporation, 
upon the Merger, and without any order or other action on the part of any 
court or otherwise, shall hold and enjoy all rights of property, franchises 
and interests in any fiduciary capacity, in the same manner and to the same 
extent as such rights, franchises and interests were held or enjoyed by SC 
Bank or NBSC at the time of the Merger. At the Effective Time, the articles 
of incorporation, bylaws and certificate of authority of the Surviving 
Corporation shall be the articles of incorporation, bylaws and certificate of 
authorization to commence banking of SC Bank immediately prior to the 
Effective Time.

          SECTION 1.2.  EFFECT ON OUTSTANDING SHARES. (a)  By virtue of the 
Merger, automatically and without any action on the part of the holder 
thereof, each share of NBSC Common Stock issued and outstanding at the 
Effective Time shall be cancelled automatically.


                                    -2-

<PAGE>

          (b)  At the Effective Time, the issued and outstanding shares of SC 
Bank Common Stock shall constitute all of the issued and outstanding shares 
of capital stock of the Surviving Corporation.

          SECTION 1.3.  ASSUMPTION OF LIABILITIES.  The Surviving Corporation 
shall be responsible for all of the liabilities of every kind and description 
of both SC Bank and NBSC existing as of the Effective Time.


                  ARTICLE II.  REPRESENTATIONS AND WARRANTIES

          SECTION 2.1.  REPRESENTATIONS AND WARRANTIES OF NBSC.  NBSC 
represents and warrants to SC Bank that the Recitals of this Plan with 
respect to NBSC are true and correct.

          SECTION 2.2.  REPRESENTATIONS AND WARRANTIES OF SC BANK.  SC Bank 
represents and warrants to NBSC that the Recitals of this Plan with respect 
to SC Bank are true and correct.


                           ARTICLE III.  COVENANTS

          SECTION 3.1.  CERTAIN FILINGS, CONSENTS AND ARRANGEMENTS.  SC Bank 
and NBSC shall (a) as soon as practicable make any filings and applications 
required to be filed in order to obtain all approvals, consents and waivers 
of governmental authorities necessary or appropriate for the consummation of 
the transactions contemplated hereby; (b) cooperate with one another (i) in 
promptly determining what filings are required to be made or approvals, 
consents or waivers are required to be obtained under any relevant federal, 
state or foreign law or regulation and (ii) in promptly making any such 
filings, furnishing information required in connection therewith and seeking 
timely to obtain any such approvals, consents or waivers; and (c) deliver to 
the other copies of the publicly available portions of all such filings and 
applications promptly after they are filed.

          SECTION 3.2.  ADDITIONAL AGREEMENTS.  Subject to the terms and
conditions herein provided, each of the parties hereto agrees to use its
reasonable best efforts to take promptly, or cause to be taken promptly, all
actions and to do promptly, or cause to be done promptly, all things necessary,
proper or advisable under applicable laws and regulations to consummate and make
effective the transactions contemplated by this Plan as soon as practicable,
including using efforts to obtain all necessary actions or non-actions,
extensions, waivers, consents and approvals from all applicable


                                    -3-

<PAGE>

governmental entities, effecting all necessary registrations, applications 
and filings (including, without limitation, filings under any applicable 
state securities laws) and obtaining any required contractual consents and 
regulatory approvals.

          SECTION 3.3.  DIRECTORS; RESIGNATIONS.  The parties agree that the 
directors of SC Bank immediately prior to the Effective Time shall continue 
to be the directors of the Surviving Corporation at and after the Effective 
Time. NBSC shall cause to be delivered to SC Bank at the Effective Time the 
resignations of the members of its Board of Directors.


                   ARTICLE IV.  CONDITIONS TO CONSUMMATION

          SECTION 4.1.  CONSENTS; APPROVALS.  SC Bank and NBSC shall have 
procured, as necessary, the required approvals, consents or waivers with 
respect to this Agreement and the transactions contemplated hereby by (i) the 
Board of Governors of the Federal Reserve Board, and (ii) the California 
Commissioner of Financial Institutions pursuant to California Law, and all 
applicable statutory waiting periods shall have expired; and the parties 
shall have procured all other regulatory approvals, consents or waivers of 
governmental authorities that are necessary or appropriate to the 
consummation of the transactions contemplated by this Agreement.


                           ARTICLE V.  TERMINATION

          SECTION 5.1.  TERMINATION.  This Plan may be terminated, and the 
Merger abandoned, prior to the Effective Date, by SC Bank or NBSC, upon 
written notice to the other party, if either (i) any approval, consent or 
waiver of a governmental authority required to permit consummation of the 
Merger or any transaction necessary to consummate the Merger shall have been 
denied or (ii) any governmental authority of competent jurisdiction shall 
have issued a final, unappealable order enjoining or otherwise prohibiting 
consummation of the Merger or any transaction necessary to consummate the 
Merger.

          SECTION 5.2.  EFFECT OF TERMINATION.  In the event of the termination
of this Plan as provided above, this Plan shall thereafter become void and,
subject to the provisions of Section 7.1 hereof, there shall be no liability on
the part of any party hereto or their respective officers or directors, except
that any such termination shall be without prejudice to the rights of any party
hereto arising out of the willful


                                    -4-

<PAGE>

breach by any other party of any covenant or willful misrepresentation 
contained in this Plan or the Parent Plan.


                ARTICLE VI.  EFFECTIVE DATE AND EFFECTIVE TIME

          SECTION 6.1.  EFFECTIVE DATE AND EFFECTIVE TIME.  Upon the 
satisfaction or waiver of all conditions to the consummation of the Merger, 
all documents required to effect the Merger shall be executed in accordance 
with all appropriate legal requirements and shall be filed as required by 
law, and the Merger provided for herein shall become effective upon such 
filing.  The "Effective Date" and "Effective Time" shall be the date and 
time, respectively, at which the Merger shall become effective in accordance 
with Section 4887 of the California Financial Code.


                          ARTICLE VII.  OTHER MATTERS

          SECTION 7.1.  SURVIVAL.  Only those agreements and covenants of the 
parties that are by their terms applicable in whole or in part after the 
Effective Time shall survive the Effective Time.  All other representations, 
warranties, agreements and covenants shall be deemed to be conditions of the 
Plan and shall not survive the Effective Time.  If the Plan shall be 
terminated, the agreements of the parties in Section 5.2, this Section 7.1, 
Section 7.5 and Section 7.6 hereof shall survive such termination.

          SECTION 7.2.  WAIVER.  Prior to the Effective Time, any provision 
of this Plan may be: (i) waived by the party benefitted by the provision; or 
(ii) amended or modified at any time (including the structure of the 
transaction) by an agreement in writing between the parties hereto approved 
by their respective Boards of Directors.

          SECTION 7.3.  COUNTERPARTS.  This Plan may be executed in 
counterparts, each of which shall be deemed to constitute an original, but 
all of which together shall constitute one and the same instrument.

          SECTION 7.4.  GOVERNING LAW.  This Plan shall be governed by, and 
interpreted in accordance with, the laws of the State of California, and to 
the extent applicable, federal law.

          SECTION 7.5.  WAIVER OF JURY TRIAL.  EACH OF THE PARTIES HERETO 
HEREBY IRREVOCABLY WAIVES ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL 
PROCEEDING ARISING OUT OF OR RELATED TO THIS PLAN OR THE TRANSACTIONS 
CONTEMPLATED HEREBY.


                                    -5-

<PAGE>

          SECTION 7.6.  EXPENSES.  Each party hereto will bear all expenses 
incurred by it in connection with this Plan and the transactions contemplated 
hereby.

          SECTION 7.7.  NOTICES.  All notices, requests, acknowledgments and 
other communications hereunder to a party shall be in writing and shall be 
deemed to have been duly given when delivered by hand, telecopy, telegram or 
telex (confirmed in writing) to such party at its address set forth below or 
such other address as such party may specify by notice to the other party 
hereto.

          If to NBSC, to:

               National Bank of Southern California
               4100 Newport Place
               Newport Beach, California 92660
               Telecopier:(714) 863-2336
               Attention:  Mark H. Stuenkel


          If to SC Bank, to:

               Southern California Bank
               4100 Newport Place
               Newport Beach, California 92660
               Telecopier:(714) 863-2336
               Attention:  Mark H. Stuenkel


          SECTION 7.8.  ENTIRE AGREEMENT; ETC.  This Plan represents the 
entire understanding of the parties hereto with reference to the transactions 
contemplated hereby and supersedes any and all other oral or written 
agreements heretofore made.  All terms and provisions of this Plan shall be 
binding upon and shall inure to the benefit of the parties hereto and their 
respective successors and assigns.  Nothing in this Plan is intended to 
confer upon any other Person any rights or remedies of any nature whatsoever 
under or by reason of this Plan.

          SECTION 7.9.  ASSIGNMENT.  This Plan may not be assigned by any 
party hereto without the written consent of the other parties.


                                    -6-

<PAGE>

          IN WITNESS WHEREOF, the parties hereto have caused this Plan to be 
executed by their duly authorized officers as of the day and year first above 
written.

                                   SOUTHERN CALIFORNIA BANK


                                   By:
                                      ----------------------------------
                                      Name:  Mark H. Stuenkel
                                      Title: President

                                   NATIONAL BANK OF SOUTHERN CALIFORNIA



                                   By:
                                      ----------------------------------
                                      Name:  William H. Jacoby
                                      Title: Chairman



                                   By:
                                      ----------------------------------
                                      Name:  Mark H. Stuenkel
                                      Title: President



                                    -7-