<PAGE>   1
                                                                  EXHIBIT 10(K)

                                    UST CORP.

                        SENIOR OFFICER SEVERANCE PAY PLAN
                       RESTATED EFFECTIVE DECEMBER 8, 1998

I.    PURPOSE

      This Plan is intended to provide salary continuation to certain designated
      Senior Officers of UST Corp. (the "Company") in the event that their
      employment is terminated as provided hereafter due to a reduction in force
      or a corporate restructuring or following a Change of Control.

II.   ELIGIBILITY TO PARTICIPATE

      A.    In order to be eligible to participate in this Plan, and employee
            must be currently designated, in writing, by the Chief Executive
            Officer of the Company or his designee as an "Senior Officer" for
            purposes of this Plan.

III.  QUALIFYING EVENTS

      A.    An employee eligible to participate in this Plan under Section II
            above (a "participating employee") is entitled to receive benefits
            under the Plan only if all of the following three conditions are
            met: (i) the employee is on the Company's active payroll or on a
            leave of absence that has been approved in writing, with guaranteed
            reinstatement, at the time his/her employment terminates; and (ii)
            termination occurs in one of the following circumstances:

            1.    The participating employee's employment is terminated as a
                  result of the elimination of his/her position with the Company
                  in conjunction with a reduction in force or a corporate
                  restructuring and the employee is not offered employment in a
                  comparable position with the Company or one of its Affiliates;
                  or

            2.    The employee's employment is terminated other than for Cause
                  by the Company within twelve (12) months following a Change in
                  Control; and

            3.    The employee is not then covered by another severance pay plan
                  or by an individual employment agreement or other severance
                  arrangement providing benefits that in the aggregate are
                  comparable to or exceed those for which the employee would
                  otherwise be eligible under this Plan; and (iii) the
                  participating employee executes the release of claims attached
                  hereto and marked "A" (the "Employee Release") within
                  forty-five (45)
<PAGE>   2

                  days of the date on which he/she receives notice of
                  termination of his/her employment, and does not timely revoke
                  it.

IV.   EXCLUSIONS

      A.    The following are examples of events in which an employee would not
            qualify for benefits under this Plan:

            1.    The employee resigns or otherwise voluntarily leaves his/her
                  employment with the Company; or

            2.    The employee's employment is terminated by the Company for
                  Cause; or

            3.    The employee is offered comparable employment at
                  the time of the elimination of his/her position; or

            4.    The employee is temporarily laid off; or

            5.    The employee is on a leave of absence which has not been
                  approved in writing or as to which reinstatement is not
                  guaranteed; or

            6.    The employee elects not to execute the Employee Release.

      B.    This Plan does not constitute a contract of employment for a
            specific term or otherwise alter the at-will nature of the
            employment relationship between any employee and the Company.

V.    BENEFITS

      A.    Benefits under this Plan are determined by length of service, as
            follows:

            1.    Six (6) months' pay, at the participating employee's final
                  base rate of pay, if the participating employee has not more
                  than three (3) full years of service with the Company as of
                  the date employment terminates; or

            2.    Nine (9) months' pay, at the participating employee's final
                  base rate of pay, if the participating employee has more than
                  three (3) full years of service, but not more than six (6)
                  full years of service, with the Company as of the date his/her
                  employment terminates.

            3.    Twelve (12) months' pay, at the participating employee's final
                  base rate of pay, if the participating employee has more than
                  six (6) full years of service with the Company as of the date
                  his/her employment terminates.

      B.    Provided that the participating employee elects to receive benefits
            as salary continuation under option 2 of paragraph D of this Section
            V, and provided further that the participating employee is currently
            enrolled in, and exercises his/her right to continue coverage, under
            the Company's group heath plan in accordance with applicable federal
            law ("COBRA"), then, for the duration of the period in which the
            participating employee is receiving such salary continuation or, if
            earlier, until the date the participating employee ceases to be
            eligible for continued coverage in accordance with COBRA, the
            Company shall continue to pay that share of the premium cost of the
            participating employee's coverage and that of his/her eligible
            dependents under the Company's group health plan that it pays for
            active employees of the Company and their eligible dependents
            generally or, following a Change of Control, the amount the Company
            was paying for active employees of

                                      -2-
<PAGE>   3
            the Company and their eligible dependents generally immediately
            prior to such Change of Control if greater.

      C.    For purposes of determining the length of service of a participating
            employee hereunder, service with the Company which occurred prior to
            a break in service of two (2) years or more shall not be included.

      D.    Benefits under Section V.A for which a participating employee is
            eligible shall be reduced by all taxes and other amounts which the
            Company is required to withhold under applicable law and shall be
            payable, at the participating employee's election, (1) in a single
            lump sum within thirty (30) days following the effective date of the
            Employee Release or (2) as salary continuation payable at the
            Company's regular payroll periods and in accordance with its regular
            payroll practices commencing on the next payday immediately
            following the effective date of the Employee Release, but
            retroactive to the date of termination of the participating
            employee's employment.

      E.    Benefits otherwise payable under this Plan shall be reduced by any
            amounts to which the employee is entitled under applicable law as a
            result of the termination of his/her employment.

      F.    The Company pays the full cost of benefits provided under this Plan
            from the Company's general assets.

      G.    Benefits under this Plan are not assignable or subject to
            alienation. Likewise, benefits are not subject to attachments by
            creditors or through legal process against the Company or any
            employee.

      H.    Notwithstanding anything to the contrary contained herein, any and
            all payments to be provided hereunder to or on behalf of any
            participating employee are subject to reduction to the extent
            required by applicable statutes, regulations, rules and directives
            of federal, state and other governmental and regulatory bodies
            having jurisdiction over the Company and/or any of its Affiliates.

VI.   DEFINITIONS

      A.    Words or phrases which are initially capitalized or within quotation
            marks shall have the meanings provided in this Section VI and as
            provided elsewhere herein. For purposes of this Plan, the following
            definitions apply:

            1.    An "Affiliate" means any individual, corporation or other
                  entity directly or indirectly controlling, controlled by or
                  under common control with the Company, where control may be by
                  management authority, equity interest or otherwise.

            2.    "Cause" for termination means only (i) the employee's refusal
                  to perform or gross negligence in the performance of, his/her
                  duties and responsibilities for the Company or (ii) the
                  employee's fraud, embezzlement or other material dishonesty
                  with respect to the Company or any of its Affiliates or (iii)
                  an action or omission by the employee in violation of the
                  banking or other laws governing the operations of the Company
                  and/or (iv) the employee's conviction of, or plea of no
                  contest to, a felony, each as communicated to the employee by


                                      -3-
<PAGE>   4
                  notice from the Company setting forth in reasonable detail the
                  nature of such Cause.

            3.    A "Change of Control" shall be deemed to have been consummated
                  if hereafter

                  i)    any "person", as such term used in Section 13(d) and
                        14(d) of the Securities Exchange Act of 1934 as amended
                        (the "Exchange Act") other than the Company or any of
                        its subsidiaries or affiliates or any trustee or other
                        fiduciary holding securities under an employee benefit
                        plan of the Company or any of its subsidiaries or
                        affiliates, becomes a beneficial owner (within the
                        meaning of Rule 13d-3, as amended, as promulgated under
                        the Exchange Act), directly or indirectly, of securities
                        representing twenty-five (25%) percent or more of the
                        combined voting power of the Company's then outstanding
                        securities; or

                  ii)   during any period of two consecutive years (not
                        including any period prior to the establishment of this
                        Plan), individuals who at the beginning of such period
                        constitute the Board of Directors of the Company (the
                        "Board"), and any new director (other than a director
                        designated by a person who has entered into an agreement
                        with the Company to effect a transaction described in
                        clause (i), (iii) or (iv) of this Section V.A.3) whose
                        election by the Board or nomination for election by the
                        Company's stockholders was approved by a vote of at
                        least two-thirds of the directors then still in office
                        who either were directors at the beginning of the period
                        or whose election or nomination for election was
                        previously so approved, cease for any reason to
                        constitute at least a majority thereof; or

                  iii)  the stockholders of the Company approve a merger or
                        consolidation of the Company with any other corporation,
                        other than a merger or consolidation which would result
                        in the voting securities of the Company outstanding
                        immediately prior thereto continuing to represent
                        (either by remaining outstanding or by being converted
                        into voting securities of the surviving entity) more
                        than eighty percent (80%) of the combined voting power
                        of the voting securities of the Company or such
                        surviving entity outstanding immediately after such
                        merger or consolidation; provided, however, that a
                        merger or consolidation effected to implement a
                        recapitalization of the Company (or similar transaction)
                        in which no "person" (as hereinabove defined) acquires
                        more than twenty-five percent (25%) of the combined
                        voting power of the Company's then outstanding
                        securities shall not constitute a Change of Control; or

                  iv)   the stockholders of the Company approve a plan of
                        complete liquidation of the Company; or

                  v)    there occurs a closing of a sale or other disposition by
                        the Company of all or substantially all of the Company's
                        assets.


                                       -4-
<PAGE>   5
            4.    The "Company" means UST Corp. or, following a Change of
                  Control, any successor of UST Corp.

VII.  ADMINISTRATION, CLAIMS PROCEDURE AND GENERAL INFORMATION

      A.    The Company reserves the right to amend, modify and terminate the
            Plan. Also, the Company, as the Plan administrator within the
            meaning of ERISA, reserves full discretion to administer the Plan in
            all of its details, subject to the requirements of law. The Company
            shall have such discretionary powers as are necessary to discharge
            its duties. Any interpretation or determination that the Company
            makes regarding this Plan, including without limitation
            determinations of eligibility, participation and benefits, will be
            final and conclusive, in the absence of clear and convincing
            evidence that the Company acted arbitrarily and capriciously.

      B.    Notwithstanding anything to the contrary contained herein, this Plan
            may not be modified, amended or terminated during the first twelve
            (12) months following a Change of Control and any participating
            employee who is designated as an "Senior Officer" for purposes of
            this Plan at the time of a Change of Control will remain so
            designated for twelve (12) months following that Change of Control.

      C.    If you believe you are being denied any rights under the Plans, you
            may file a claim in writing with the Company, as Plan administrator.
            If your claim is denied, in whole or in part, the Plan administrator
            will notify you in writing, giving the specific reasons for the
            decision, including specific reference to the pertinent Plan
            provisions and a description of any additional material or
            information necessary to perfect your claim and an explanation of
            why such material or information is necessary. The written notice
            will also advise you of your right to request a review of your claim
            and the steps that need to be taken if you wish to submit your claim
            for review. If the Plan administrator does not notify you of its
            decision within 90 days after it had received your claim (or within
            180 days, if special circumstances exist requiring additional time,
            and if you had been given a written explanation for the extension
            within the initial 90-day period), you should consider your claim to
            have been denied. At this time you may request a review of the
            denial of your claim.

            A request for review must be made in writing by you or your duly
            authorized representative to the Company, as Plan administrator,
            within 60 days after you have received the notice of denial. As part
            of your request, you may submit written issues and comments to the
            Plan administrator, review pertinent documents, and request a
            hearing. The Plan administrator's written decision will be made
            within 60 days (or 120 days if a hearing is held or if other special
            circumstances exist requiring more than 60 days and written notice
            of the extension is provided to you within the initial 60-day
            period) after your request has been received. Again, the decision
            will include specific reasons, including references to pertinent
            Plan provisions.


                                       -5-
<PAGE>   6
                                       "A"

                                RELEASE OF CLAIMS

      FOR AND IN CONSIDERATION OF the special payments to be made to me in
connection with my separation of employment, as set forth in UST Corp. Senior
Officer Severance Pay Plan (the "Plan"), I, on my own behalf and on behalf of my
heir, beneficiaries and representatives and all others connected with me, hereby
release and forever discharge UST Corp. (the "Company"), its subsidiaries and
affiliates, and all of their respective officers, directors, employees, agents,
representatives, successors and assigns and all others connected with them (all
collectively, the "Releasees"), both individually and in their official
capacities, from any and all liability, claims, demands, actions and causes of
action of any type (all collectively "Claims") which I have had in the past, now
have, or might now have, through the date of my execution of this Release of
Claims, in any way resulting from, arising out of or connected with my
employment or its termination or pursuant to any federal, state or local
employment law, regulation or other requirement (including without limitation
Title VII of the Civil Rights Act of 1964, as amended, the Age Discrimination in
Employment Act, as amended, the Americans with Disabilities Act, as amended, and
the Massachusetts fair employment practices act, as amended).

      Excluded from the scope of this Release of Claims is (i) any claim arising
hereafter under the terms of the Plan or under the terms of any of the Company's
other employee benefit plans (including without limitation the Company's
employee pension plan, profit sharing plan or stock ownership plan) and (ii) any
right of indemnification or contribution pursuant to the Articles of
Organization or By-Laws of the Company that I have or hereafter acquire if any
claim is assert or proceedings are brought against me by any governmental or
regulatory agency, or by any customer, creditor, employee or shareholder of the
Company, or by any self-regulatory organization, stock exchange or the like,
related or allegedly related to my having been an officer or employee of the
Company or to any of my activities as an officer or employee of the Company.

      By acceptance of or reliance on this Release of Claims, the Company
promises that neither it nor any of the other Releasees affiliated with the
Company will taken any action that is designed, specifically as to me or with
respect to a class of similarly situated former employees, to reduce or
abrogate, or may reasonably be expected to result in an abridgment or
elimination of, any rights of indemnification or contribution available to me
pursuant to the Articles of Organization or By-Laws of the Company, or under any
policy or policies of directors and officers liability insurance affording
coverage to former officers and in effect from time to time, unless any such
abridgment or elimination of rights is also generally applicable to then-current
officers and employees of the Company.

      In signing this Release of Claims, I acknowledge that I have had at least
forty-five (45) days from the date of my receipt of notice of termination of my
employment to consider the terms of this Release of Claims, that I am encouraged
by the Company to seek the advice of an attorney prior to signing this Release
of Claims and that I am signing this Release of Claims voluntarily and with a
full understanding of its terms. I understand that I may revoke this Release of
Claims at any time within
<PAGE>   7
seven (7) days of the date of my signing by written notice to the President of
the Company and that this Release of Claims will take effect only upon the
expiration of such seven-day revocation period and only if I have not timely
revoked it.

      IN WITNESS WHEREOF, I have set my hand and seal on the date written below.


Signature: _________________________________

Date Signed: _______________________________