<PAGE>

                                                                    EXHIBIT 10.6


                                                            U.K. OPTIONEE

                          PRIME RESPONSE GROUP, INC.
                           STOCK PURCHASE AGREEMENT
                           ------------------------


          AGREEMENT made this ______ day of ________________________ 199___, by
          ---------
and between Prime Response Group, Inc., a Delaware corporation, and
_________________________, Optionee under the Corporation's 1998 Stock
Option/Stock Issuance Plan.

          All capitalized terms in this Agreement shall have the meaning
assigned to them in this Agreement or in the attached Appendix.

     A.   EXERCISE OF OPTION
          ------------------

          1.  EXERCISE.  Optionee hereby purchases _____________ shares of
Common Stock (the "Purchased Shares") pursuant to that certain option (the
"Option") granted Optionee on ____________________, 199__ (the "Grant Date") to
purchase up to _______________ shares of Common Stock (the "Option Shares")
under the Plan at the exercise price of $___________ per share (the "Exercise
Price").

          2.  PAYMENT.  Concurrently with the delivery of this Agreement to the
Corporation, Optionee shall pay the Exercise Price for the Purchased Shares in
accordance with the provisions of the Option Agreement and shall deliver
whatever additional documents may be required by the Option Agreement as a
condition for exercise with respect to the Purchased Shares.

          3.  STOCKHOLDER RIGHTS.  Until such time as the Corporation exercises
the First Refusal Right, Optionee (or any successor in interest) shall have all
the rights of a stockholder (including voting, dividend and liquidation rights)
with respect to the Purchased Shares, subject, however, to the transfer
restrictions of Articles B and C.

     B.   SECURITIES LAW COMPLIANCE
          -------------------------

          1.  RESTRICTED SECURITIES.  The Purchased Shares have not been
registered under the 1933 Act and are being issued to Optionee in reliance upon
the exemption from such registration provided by SEC Rule 701 for stock
issuances under compensatory benefit plans such as the Plan. Optionee hereby
confirms that Optionee has been informed that the Purchased Shares are
restricted securities under the 1933 Act and may not be resold or transferred
unless the Purchased Shares are first registered under the Federal securities
laws or unless an exemption from such registration is available. Accordingly,
Optionee hereby acknowledges that Optionee is prepared to hold the Purchased
Shares for an indefinite period and that Optionee is aware that SEC Rule 144
issued under the 1933 Act which exempts certain resales of unrestricted
securities is not presently available to exempt the resale of the Purchased
Shares from the registration requirements of the 1933 Act.

<PAGE>

          2.  RESTRICTIONS ON DISPOSITION OF PURCHASED SHARES.  Optionee shall
make no disposition of the Purchased Shares (other than a Permitted Transfer)
unless and until there is compliance with all of the following requirements:

              (i)  Optionee shall have provided the Corporation with a written
     summary of the terms and conditions of the proposed disposition.

              (ii) Optionee shall have complied with all requirements of this
     Agreement applicable to the disposition of the Purchased Shares.

              (iii) Optionee shall have provided the Corporation with written
     assurances, in form and substance satisfactory to the Corporation, that
     (a) the proposed disposition does not require registration of the Purchased
     Shares under the 1933 Act or (b) all appropriate action necessary for
     compliance with the registration requirements of the 1933 Act or any
     exemption from registration available under the 1933 Act (including
     Rule 144) has been taken.

          The Corporation shall not be required (i) to transfer on its books any
                                ---
Purchased Shares which have been sold or transferred in violation of the
provisions of this Agreement or (ii) to treat as the owner of the Purchased
Shares, or otherwise to accord voting, dividend or liquidation rights to, any
transferee to whom the Purchased Shares have been transferred in contravention
of this Agreement.

          3.  RESTRICTIVE LEGENDS.  The stock certificates for the Purchased
Shares shall be endorsed with one or more of the following restrictive legends:

          "The shares represented by this certificate have not been
     registered under the Securities Act of 1933. The shares may not be
     sold or offered for sale in the absence of (a) an effective
     registration statement for the shares under such Act, (b) a "no
     action" letter of the Securities and Exchange Commission with respect
     to such sale or offer or (c) satisfactory assurances to the
     Corporation that registration under such Act is not required with
     respect to such sale or offer."

          "The shares represented by this certificate are subject to
     certain rights of first refusal granted to the Corporation and
     accordingly may not be sold, assigned, transferred, encumbered, or in
     any manner disposed of except in conformity with the terms of a
     written agreement dated __________________, 199____ between the
     Corporation and the registered holder of the shares (or the
     predecessor in interest to the shares). A copy of such agreement is
     maintained at the Corporation's principal corporate offices."

     C.   TRANSFER RESTRICTIONS
          ---------------------

          1.  RESTRICTION ON TRANSFER.  Purchased Shares shall not be
transferred, assigned, encumbered or otherwise disposed of in contravention of
the First Refusal Right or the Market Stand-Off.

<PAGE>

          2.  TRANSFEREE OBLIGATIONS.  Each person (other than the Corporation)
to whom the Purchased Shares are transferred by means of a Permitted Transfer
must, as a condition precedent to the validity of such transfer, acknowledge in
writing to the Corporation that such person is bound by the provisions of this
Agreement and that the transferred shares are subject to (i) the First Refusal
Right and (ii) the Market Stand-Off, to the same extent such shares would be so
subject if retained by Optionee.

          3.  MARKET STAND-OFF.

              (a)  In connection with any underwritten public offering by the
     Corporation of its equity securities pursuant to an effective registration
     statement filed under the 1933 Act, including the Corporation's initial
     public offering, Owner shall not sell, make any short sale of, loan,
     hypothecate, pledge, grant any option for the purchase of, or otherwise
     dispose or transfer for value or otherwise agree to engage in any of the
     foregoing transactions with respect to, any Purchased Shares without the
     prior written consent of the Corporation or its underwriters. Such
     restriction (the "Market Stand-Off") shall be in effect for such period of
     time from and after the effective date of the final prospectus for the
     offering as may be requested by the Corporation or such underwriters. In no
     event, however, shall such period exceed one hundred eighty (180) days and
     the Market Stand-Off shall in all events terminate two (2) years after the
     effective date of the Corporation's initial public offering.

              (b)  Owner shall be subject to the Market Stand-Off provided and
     only if the officers and directors of the Corporation are also subject to
     similar restrictions.

              (c)  Any new, substituted or additional securities which are by
     reason of any Recapitalization or Reorganization distributed with respect
     to the Purchased Shares shall be immediately subject to the Market Stand-
     Off, to the same extent the Purchased Shares are at such time covered by
     such provisions.

              (d)  In order to enforce the Market Stand-Off, the Corporation may
     impose stop-transfer instructions with respect to the Purchased Shares
     until the end of the applicable stand-off period.

     D.   RIGHT OF FIRST REFUSAL
          ----------------------

          1.  GRANT.  The Corporation is hereby granted the right of first
refusal (the "First Refusal Right"), exercisable in connection with any proposed
transfer of the Purchased Shares. For purposes of this Article D, the term
"transfer" shall include any sale, assignment, pledge, encumbrance or other
disposition of the Purchased Shares intended to be made by Owner, but shall not
include any Permitted Transfer.

          2.  NOTICE OF INTENDED DISPOSITION.  In the event any Owner of
Purchased Shares in which Optionee has vested desires to accept a bona fide
third-party offer for the transfer of any or all of such shares (the Purchased
Shares subject to such offer to be hereinafter referred to as the "Target
Shares"), Owner shall promptly (i) deliver to the Corporation written notice
(the "Disposition Notice") of the terms of the offer, including the purchase
price and the identity of the third-party offeror, and (ii) provide satisfactory
proof that the disposition of the

<PAGE>

Target Shares to such third-party offeror would not be in contravention of the
provisions set forth in Articles B and C.

          3.  EXERCISE OF THE FIRST REFUSAL RIGHT.  The Corporation shall, for a
period of twenty-five (25) days following receipt of the Disposition Notice,
have the right to repurchase any or all of the Target Shares subject to the
Disposition Notice upon the same terms as those specified therein or upon such
other terms (not materially different from those specified in the Disposition
Notice) to which Owner consents. Such right shall be exercisable by delivery of
written notice (the "Exercise Notice") to Owner prior to the expiration of the
twenty-five (25)-day exercise period. If such right is exercised with respect to
all the Target Shares, then the Corporation shall effect the repurchase of such
shares, including payment of the purchase price, not more than five (5) business
days after delivery of the Exercise Notice; and at such time the certificates
representing the Target Shares shall be delivered to the Corporation.

          Should the purchase price specified in the Disposition Notice be
payable in property other than cash or evidences of indebtedness, the
Corporation shall have the right to pay the purchase price in the form of cash
equal in amount to the value of such property.  If Owner and the Corporation
cannot agree on such cash value within ten (10) days after the Corporation's
receipt of the Disposition Notice, the valuation shall be made by an appraiser
of recognized standing selected by Owner and the Corporation or, if they cannot
agree on an appraiser within twenty (20) days after the Corporation's receipt of
the Disposition Notice, each shall select an appraiser of recognized standing
and the two (2) appraisers shall designate a third appraiser of recognized
standing, whose appraisal shall be determinative of such value.  The cost of
such appraisal shall be shared equally by Owner and the Corporation.  The
closing shall then be held on the later of (i) the fifth (5th) business day
following delivery of the Exercise Notice or (ii) the fifth (5th) business day
after such valuation shall have been made.

          4.  NON-EXERCISE OF THE FIRST REFUSAL RIGHT.  In the event the
Exercise Notice is not given to Owner prior to the expiration of the twenty-five
(25)-day exercise period, Owner shall have a period of thirty (30) days
thereafter in which to sell or otherwise dispose of the Target Shares to the
third-party offeror identified in the Disposition Notice upon terms (including
the purchase price) no more favorable to such third-party offeror than those
specified in the Disposition Notice; provided, however, that any such sale or
disposition must not be effected in contravention of the provisions of Articles
B and C. The third-party offeror shall acquire the Target Shares free and clear
of the First Refusal Right, but the acquired shares shall remain subject to the
provisions of Article B and Paragraph C.3. In the event Owner does not effect
such sale or disposition of the Target Shares within the specified thirty
(30)-day period, the First Refusal Right shall continue to be applicable to any
subsequent disposition of the Target Shares by Owner until such right lapses.

          5.  PARTIAL EXERCISE OF THE FIRST REFUSAL RIGHT.  In the event the
Corporation makes a timely exercise of the First Refusal Right with respect to a
portion, but not all, of the Target Shares specified in the Disposition Notice,
Owner shall have the option, exercisable by written notice to the Corporation
delivered within five (5) business days after Owner's receipt of the Exercise
Notice, to effect the sale of the Target Shares pursuant to either of the
following alternatives:

<PAGE>

              (i)  sale or other disposition of all the Target Shares to the
     third-party offeror identified in the Disposition Notice, but in full
     compliance with the requirements of Paragraph D.4, as if the Corporation
     did not exercise the First Refusal Right; or

              (ii) sale to the Corporation of the portion of the Target Shares
     which the Corporation has elected to purchase, such sale to be effected in
     substantial conformity with the provisions of Paragraph D.3. The First
     Refusal Right shall continue to be applicable to any subsequent disposition
     of the remaining Target Shares until such right lapses.

          Owner's failure to deliver timely notification to the Corporation
shall be deemed to be an election by Owner to sell the Target Shares pursuant to
alternative (i) above.

          6.  RECAPITALIZATION/REORGANIZATION.

              (a)  Any new, substituted or additional securities or other
     property which is by reason of any Recapitalization distributed with
     respect to the Purchased Shares shall be immediately subject to the First
     Refusal Right, but only to the extent the Purchased Shares are at the time
     covered by such right.

              (b)  In the event of a Reorganization, the First Refusal Right
     shall remain in full force and effect and shall apply to the new capital
     stock or other property received in exchange for the Purchased Shares in
     consummation of the Reorganization, but only to the extent the Purchased
     Shares are at the time covered by such right.

          7.  LAPSE.  The First Refusal Right shall lapse upon the earliest to
occur of (i) the first date on which shares of the Common Stock are held of
record by more than five hundred (500) persons, (ii) a determination is made by
the Board that a public market exists for the outstanding shares of Common Stock
or (iii) a firm commitment underwritten public offering, pursuant to an
effective registration statement under the 1933 Act, covering the offer and sale
of the Common Stock in the aggregate amount of at least ten million dollars
($10,000,000). However, the Market Stand-Off shall continue to remain in full
force and effect following the lapse of the First Refusal Right.

     E.   GENERAL PROVISIONS
          ------------------

          1.  ASSIGNMENT.  The Corporation may assign the First Refusal Right to
any person or entity selected by the Board, including (without limitation) one
or more stockholders of the Corporation.

          2.  NO EMPLOYMENT OR SERVICE CONTRACT.  Nothing in this Agreement or
in the Plan shall confer upon Optionee any right to continue in Service for any
period of specific duration or interfere with or otherwise restrict in any way
the rights of the Corporation (or any Parent or Subsidiary employing or
retaining Optionee) or of Optionee, which rights are hereby expressly reserved
by each, to terminate Optionee's Service at any time for any reason, with or
without cause.

<PAGE>

          3.  NOTICES.  Any notice required to be given under this Agreement
shall be in writing and shall be deemed effective upon personal delivery or upon
deposit in the U.S. mail, registered or certified, postage prepaid and properly
addressed to the party entitled to such notice at the address indicated below
such party's signature line on this Agreement or at such other address as such
party may designate by ten (10) days advance written notice under this paragraph
to all other parties to this Agreement.

          4.  NO WAIVER.  The failure of the Corporation in any instance to
exercise the First Refusal Right shall not constitute a waiver of any other
repurchase rights and/or rights of first refusal that may subsequently arise
under the provisions of this Agreement or any other agreement between the
Corporation and Optionee. No waiver of any breach or condition of this Agreement
shall be deemed to be a waiver of any other or subsequent breach or condition,
whether of like or different nature.

          5.  CANCELLATION OF SHARES.  If the Corporation shall make available,
at the time and place and in the amount and form provided in this Agreement, the
consideration for the Purchased Shares to be repurchased in accordance with the
provisions of this Agreement, then from and after such time, the person from
whom such shares are to be repurchased shall no longer have any rights as a
holder of such shares (other than the right to receive payment of such
consideration in accordance with this Agreement). Such shares shall be deemed
purchased in accordance with the applicable provisions hereof, and the
Corporation shall be deemed the owner and holder of such shares, whether or not
the certificates therefor have been delivered as required by this Agreement.

     F.   MISCELLANEOUS PROVISIONS
          ------------------------

          1.  OPTIONEE UNDERTAKING.  Optionee hereby agrees to take whatever
additional action and execute whatever additional documents the Corporation may
deem necessary or advisable in order to carry out or effect one or more of the
obligations or restrictions imposed on either Optionee or the Purchased Shares
pursuant to the provisions of this Agreement.

          2.  AGREEMENT IS ENTIRE CONTRACT.  This Agreement constitutes the
entire contract between the parties hereto with regard to the subject matter
hereof. This Agreement is made pursuant to the provisions of the Plan and shall
in all respects be construed in conformity with the terms of the Plan.

          3.  GOVERNING LAW.  This Agreement shall be governed by, and construed
in accordance with, the laws of the State of California without resort to that
State's conflict-of-laws rules.

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

          5.  SUCCESSORS AND ASSIGNS.  The provisions of this Agreement shall
inure to the benefit of, and be binding upon, the Corporation and its successors
and assigns and upon Optionee, Optionee's permitted assigns and the legal
representatives, heirs and legatees of

<PAGE>

Optionee's estate, whether or not any such person shall have become a party to
this Agreement and have agreed in writing to join herein and be bound by the
terms hereof.

<PAGE>

          IN WITNESS WHEREOF, the parties have executed this Agreement on the
day and year first indicated above.

                                 PRIME RESPONSE GROUP, INC.


                                 By:
                                     ---------------------------------

                                 Title:
                                        ------------------------------

                                 Address:
                                          ----------------------------

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





                                 -------------------------------------
                                 OPTIONEE

                                 Address:
                                          ----------------------------

                                          ----------------------------
<PAGE>

                            SPOUSAL ACKNOWLEDGMENT


          The undersigned spouse of Optionee has read and hereby approves the
foregoing Stock Purchase Agreement.  In consideration of the Corporation's
granting Optionee the right to acquire the Purchased Shares in accordance with
the terms of such Agreement, the undersigned hereby agrees to be irrevocably
bound by all the terms of such Agreement.



                                 -------------------------------------
                                 OPTIONEE'S SPOUSE

                                 Address:
                                          ----------------------------

                                          ----------------------------
<PAGE>

                                   APPENDIX
                                   --------


          The following definitions shall be in effect under the Agreement:

     A.   AGREEMENT shall mean this Stock Purchase Agreement.
          ---------

     B.   BOARD shall mean the Corporation's Board of Directors.
          -----

     C.   CODE shall mean the Internal Revenue Code of 1986, as amended.
          ----

     D.   COMMON STOCK shall mean the Corporation's common stock.
          ------------

     E.   CORPORATION shall mean Prime Response Group, Inc., a Delaware
          -----------
corporation.

     F.   DISPOSITION NOTICE shall have the meaning assigned to such term in
          ------------------
Paragraph D.2.

     G.   EXERCISE NOTICE shall have the meaning assigned to such term in
          ---------------
Paragraph D.3.

     H.   EXERCISE PRICE shall have the meaning assigned to such term in
          --------------
    Paragraph A.1.

     I.   FAIR MARKET VALUE of a share of Common Stock on any relevant date,
          -----------------
prior to the initial public offering of the Common Stock, shall be determined by
the Plan Administrator after taking into account such factors as it shall deem
appropriate.

     J.   FIRST REFUSAL RIGHT shall mean the right granted to the Corporation in
          -------------------
accordance with Article D.

     K.   GRANT DATE shall have the meaning assigned to such term in Paragraph
          ----------
A.1.

     L.   GRANT NOTICE shall mean the Notice of Grant of Stock Option pursuant
          ------------
to which Optionee has been informed of the basic terms of the Option.

     M.   MARKET STAND-OFF shall mean the market stand-off restriction specified
          ----------------
in Paragraph C.3.

     N.   1933 ACT shall mean the Securities Act of 1933, as amended.
          --------

     O.   1934 ACT shall mean the Securities Exchange Act of 1934, as amended.
          --------

     P.   NON-STATUTORY OPTION shall mean an option not intended to satisfy the
          --------------------
requirements of Code Section 422.

     Q.   OPTION shall have the meaning assigned to such term in Paragraph A.1.
          ------

     R.   OPTION AGREEMENT shall mean all agreements and other documents
          ----------------
evidencing the Option.

                                      A-1
<PAGE>

     S.   OPTIONEE shall mean the person to whom the Option is granted under the
          --------
Plan.

     T.   OWNER shall mean Optionee and all subsequent holders of the Purchased
          -----
Shares who derive their chain of ownership through a Permitted Transfer from
Optionee.

     U.   PARENT shall mean any corporation (other than the Corporation) in an
          ------
unbroken chain of corporations ending with the Corporation, provided each
corporation in the unbroken chain (other than the Corporation) owns, at the time
of the determination, stock possessing fifty percent (50%) or more of the total
combined voting power of all classes of stock in one of the other corporations
in such chain.

     V.   PERMITTED TRANSFER shall mean (i) a gratuitous transfer of the
          ------------------
Purchased Shares, provided and only if Optionee obtains the Corporation's prior
written consent to such transfer, (ii) a transfer of title to the Purchased
Shares effected pursuant to Optionee's will or the laws of intestate succession
following Optionee's death or (iii) a transfer to the Corporation in pledge as
security for any purchase-money indebtedness incurred by Optionee in connection
with the acquisition of the Purchased Shares.

     W.   PLAN shall mean the Corporation's 1998 Stock Option/Stock Issuance
          ----
Plan.

     X.   PLAN ADMINISTRATOR shall mean either the Board or a committee of the
          ------------------
     Board acting in its capacity as administrator of the Plan.

     Y.   PURCHASED SHARES shall have the meaning assigned to such term in
          ----------------
Paragraph A.1.

     Z.   RECAPITALIZATION shall mean any stock split, stock dividend,
          ----------------
recapitalization, combination of shares, exchange of shares or other change
affecting the Corporation's outstanding Common Stock as a class without the
Corporation's receipt of consideration.

     AA.  REORGANIZATION shall mean any of the following transactions:
          --------------

         (i)  a merger or consolidation in which the Corporation is not the
     surviving entity,

         (ii) a sale, transfer or other disposition of all or substantially all
     of the Corporation's assets,

         (iii) a reverse merger in which the Corporation is the surviving entity
     but in which the Corporation's outstanding voting securities are
     transferred in whole or in part to a person or persons different from the
     persons holding those securities immediately prior to the merger, or

         (iv) any transaction effected primarily to change the state in which
     the Corporation is incorporated or to create a holding company structure.

     BB.  SEC shall mean the Securities and Exchange Commission.
          ---

                                      A-2
<PAGE>

     CC.  SERVICE shall mean the Optionee's performance of services for the
          -------
Corporation (or any Parent or Subsidiary) in the capacity of an employee,
subject to the control and direction of the employer entity as to both the work
to be performed and the manner and method of performance, a non-employee member
of the board of directors or an independent consultant.

     DD.  SUBSIDIARY shall mean any corporation (other than the Corporation) in
          ----------
an unbroken chain of corporations beginning with the Corporation, provided each
corporation (other than the last corporation) in the unbroken chain owns, at the
time of the determination, stock possessing fifty percent (50%) or more of the
total combined voting power of all classes of stock in one of the other
corporations in such chain.

     EE. TARGET SHARES shall have the meaning assigned to such term in Paragraph
         -------------
D.2.

                                      A-3