Document:

<PAGE>
                                                                    Exhibit 4.18

                                                                October 21, 2002

Richard Stewart, CEO
Amarin Corporation plc
7 Curzon Street
London, W1J 5HG

Dear Mr Stewart

         We are pleased to confirm the arrangements under which Security
Research Associates, Inc. ("SRA") is engaged by Amarin Corporation plc (the
"Company") as financial advisor and non-exclusive placement agent on a
"best-efforts" basis in connection with a proposed private placement of up to
$25 million of ordinary shares, par value Pound Sterling 1 per share, of the
Company (the "Ordinary Shares") to be issued by the Company in accordance with
the proposed terms set forth in Annex A (the "Financing").

         During the term of our engagement, we will provide you with financial
advice and assistance in connection with the Financing, which may include
performing valuation analyses and assisting you in negotiating the financial
aspects of the transaction. During the term of our engagement, we will also
identify and contact potential investors and assist in the preparation and
review of a private placement memorandum and other documents related to the
Financing.

         In the event the Financing is consummated, the Company agrees to pay to
SRA a transaction fee (the "Transaction Fee") consisting of (i) 7% of the gross
proceeds from the Financing received by the Company from investors introduced by
SRA to the Company (the "SRA Investors") prior to the Closing Date, and (ii) 5
year warrants to acquire a number of shares of the Company's Ordinary Shares
equal to 7% of the aggregate gross proceeds from the Financing received by the
Company from SRA Investors divided by the price per share of the Company's
securities paid by the SRA Investors. The warrants will have an exercise price
which will be the same as the per share price paid by the SRA Investors in the
Financing. The warrants shall be exercisable no earlier than one year from the
date of closing of the Financing (the "Closing Date"). The warrants shall be
issued pursuant to a definitive warrant agreement containing customary
provisions including registration rights anti-dilution provisions which comply
with NASD regulatory requirements. The Company will provide the same
registration rights to SRA as it provides to the SRA Investors.

         The Company also agrees to reimburse SRA periodically, upon request, or
upon termination of our services pursuant to this letter (the "agreement"), for
our reasonable and reasonably documented out-of-pocket expenses, incurred in
connection with our financial advisory services and the Financing, including the
reasonable fees and expenses of legal counsel, travel expenses and printing. All
such out-of-pocket fees and expenses shall not exceed a combined aggregate
amount of $10,000.

         Please note that any written or oral opinion or advice provided by SRA
in connection

                                  Page 1 of 4

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with our engagement is exclusively for the information of the Board of Directors
and senior management of the Company, and may not be disclosed to any third
party (other than the Company's legal, accounting or other advisors, who shall
have been instructed with respect to the confidentiality of such advice) or
circulated or referred to publicly without our prior written consent, except as
to the extent required by law, judicial or administrative process or regulatory
demand.

         As you know, SRA may, from time to time, effect transactions in the
Company's stock, for its own account or the account of customers, and hold
positions in securities or options on securities of the Company.

         The term of this Agreement shall extend to the Closing Date. The
Company or SRA shall be entitled to terminate this Agreement before the Closing
Date on written notice to the other party at the address set forth for such
party on the signature page hereof. In the event of the termination of this
Agreement, SRA shall be entitled to be paid its existing reasonable
out-of-pocket expenses subject to the terms described above. The confidentiality
provisions of this Agreement shall be unaffected by the termination of this
agreement. The Company shall not be obligated to reimburse any expenses incurred
by SRA or its advisors with respect to activities undertaken after notification
of termination is given. [In the event this Agreement is terminated and prior to
the expiration of 12 months from the date of such termination, an agreement is
entered into by the Company with respect to any transaction contemplated by this
agreement with a third party introduced to the Company by SRA who was not known
to the Company prior to such introduction, SRA will be entitled to the
transaction fee set forth above. Upon the termination or expiration of this
Agreement, SRA shall provide the Company with a list of those entities
introduced to the Company by SRA with respect to the Financing.

         SRA is an independent contractor and non-exclusive placement agent of
the Company. SRA will not have any right or authority to bind the Company or
otherwise create any obligations of any kind on behalf of the Company and will
make no representation to any third party to the contrary. The Company and SRA
each acknowledge and understand that SRA will provide services on a
non-exclusive basis. In addition, the Company and SRA each acknowledge and
understand that the Company may utilize the services of other placement agents
and solicitors in connection with arranging or placing any portion of the
Financing.

         During the term of this Agreement and thereafter, each of the Company
and SRA agrees to keep confidential and not disclose to any third party any
confidential information of the other party, and to use such confidential
information only in connection with the engagement hereunder; provided, however,
the foregoing will not prohibit disclosures (i) to the parties' employees,
agents and other representatives to the extent necessary to enable the Company
or SRA to perform its responsibilities under this Agreement, (ii) to the extent
required by law, judicial or administrative process or regulatory demand, or
(iii) with respect to matters which become public other than by the actions of
the disclosing party hereunder. This section will survive the termination of
this Agreement.

         Each of the Company and SRA agrees of conduct the Financing in a manner
intended to qualify for the exemption from the registration requirements of the
Securities Act of 1933, as amended (the "Act"), provided by Section 4(2) of the
Act. Each of the Company and SRA agrees to limit offers to sell, and
solicitations of offers to buy, securities of the Company in connection with the
Financing to persons reasonably believed by it to be "qualified institutional

                                  Page 2 of 4

<PAGE>

buyers" as such term is defined in Rule 144A under the Act and "accredited
investors" as such term is defined in Rule 501(a) of Regulation D promulgated
under the Act.

         Each of the Company and SRA agrees that any offers it makes in
connection with the Financing will be made only to prospective purchasers on an
individual basis and that it will not engage in any form of general solicitation
or general advertising (within the meaning of Rule 502 under the Act) in
connection with the Financing. Each of the Company and SRA agrees to conduct the
Financing in a manner intended to comply with the registration or qualification
requirements, or available exemptions therefrom, under applicable state "blue
sky" laws and applicable securities laws of other jurisdictions.

         The Company may decline to consummate the Financing with any
prospective purchaser in the Company's sole discretion.

         Any dispute arising out of this Agreement shall be resolved in an
arbitration conducted pursuant to the rules of the National Association of
Securities Dealers, Inc. in San Francisco, CA.

         Please confirm that the foregoing is in accordance with your
understanding by signing and returning to us the enclosed copy of this
Agreement, which shall become a binding agreement upon our receipt. We are
delighted to accept this engagement and look forward to working with you on this
assignment.

Very truly yours,                               Confirmed by:

SECURITY RESEARCH ASSOCIATES, INC.              AMARIN CORPORATION PLC
80 E. Sir Francis Drake Boulevard, Suite 3F     7 Curzon Street, Mayfair
Larkspur, CA 94939                              London W1J 5HG
U.S                                             U.K

By: /s/ Brian G. Swift                          By: /s/ Richard A. B. Stewart
    ----------------------------                    ----------------------------
    Brian G. Swift                                  Richard A. B. Stewart
    Chairman                                        Chief Executive Officer

Date: 1/9/03                                    Date: 1/9/03

                                  Page 3 of 4

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                                     ANNEX A

                                                                    CONFIDENTIAL

  TERM SHEET FOR PRIVATE PLACEMENT OF ORDINARY SHARES OF AMARIN CORPORATION PLC

INVESTORS:       "qualified institutional buyers" (as defined in Rule 144A under
                 the Act) and "accredited investors" (as defined in Rule 501(a)
                 of Regulation D under the Act) acceptable to the Company.

TOTAL AMOUNT:    Up to $25 million by the sale of Ordinary Shares or as mutually
                 agreed.

STOCK PRICE:     To be negotiated between the Company and the investors who
                 purchase Ordinary Shares of the Company in the Financing, but,
                 in no event shall the sale price per Ordinary Share be less
                 than the price per Ordinary Share equal to 90% of the average
                 closing prices of the Company's American depositary receipts on
                 NASDAQ over the five trading days immediately prior to the
                 Closing Date.

REGISTRATION:    The Company shall enter into a registration rights agreement
                 (the "Registration Rights Agreement") with each of the
                 investors who purchase Ordinary Shares of the Company in the
                 Financing. In addition to other customary terms and provisions,
                 the Registration Rights Agreement will require the Company to
                 use its reasonable efforts to file within ninety (90) days of
                 the Closing Date with the Securities and Exchange Commission
                 (the "SEC") a registration statement on Form F-1 or F-3 (or
                 other appropriate form) for all shares of the Company's
                 Ordinary Shares sold in this Financing and the Ordinary Shares
                 underlying the warrants issued to SRA as part of the
                 Transaction Fee. The Registration Rights Agreement will also
                 require the Company to use its reasonable efforts to have such
                 registration statement declared effective at the earlier of one
                 hundred and eighty (180) days from the Closing Date orten (10)
                 days after receiving a no-review status from the SEC. Finally,
                 the Registration Rights Agreement will only require the Company
                 to keep such registration statement effective for a period of
                 one (1) year from the Closing Date.

CLOSING DATE:    Mutual agreement between the Company and the prospective
                 purchasers, but not later than November 29, 2002.

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                                                                   Exhibit 4.19

EXECUTION COPY

      AGREEMENT ("Agreement") dated 27th January 2003 among Amarin Corporation
plc ("Company"), Monksland Holdings BV ("Monksland") and Elan International
Services Limited ("EISL" and, together with Monksland, the "Shareholder").

                                  INTRODUCTION

     Monksland and EISL hold ordinary shares, par value Pound Sterling 1 per
share ("Ordinary Shares") and 3% convertible preference shares ("Preference
Shares") of the Company, all or part of which shares are subject to the terms of
the (a) Second Subscription Agreement, dated November 1999, among the Company
(formerly named Ethical Holdings plc), Monksland and Elan Corporation plc ("1999
Subscription Agreement") and (b) Convertible Term Loan Agreement, dated October
21, 1998, between the Company (formerly named Ethical Holdings plc) and
Monksland ("CTLA"). Under the 1999 Subscription Agreement and the CTLA, the
Company is obligated to register with the United States Securities and Exchange
Commission certain Ordinary Shares held by Monksland and EISL.

      The Company and EISL entered into an Agreement dated 28 March 2002
pursuant to which EISL agreed not to convert 2,000,000 Preference Shares into
Ordinary Shares until after 1 December 2002. EISL now wishes to convert such
Preference Shares and will present a conversion notice to the Company in the
form set out in schedule 2.

      Simultaneously herewith, the Company, EISL and Monksland are entering into
an Amendment No. 1 to Registration Rights Agreement And Waiver (the
"Registration Rights Agreement") relating to the Registration Rights Agreement
between the Company and Monksland dated as of 21 October 1998.

      The Company is conducting a private placement ("Private Placement") of
Ordinary Shares pursuant to an Amended Confidential Private Placement Memorandum
dated 10 December 2002, as supplemented by a letter dated January 2003, which
together are attached as Exhibit B hereto. In connection with such Private
Placement, the Company is undertaking to the investors ("Investors") therein to
use its reasonable efforts to file a registration statement ("Registration
Statement") with the Securities and Exchange Commission, within 90 days of
completion of the Private Placement, on Form F-3 or such other form as is
appropriate and use its reasonable efforts to cause such registration statement
to be declared effective.

      The Shareholder may also enter into a share purchase agreement in
substantially the form of Exhibit A hereto (the "Share Purchase Agreement") with
certain Investors, pursuant to which such Investors may acquire up to 944,124
Ordinary Shares held by the Shareholder.

      At the same time as entering into this Agreement EISL and the Company
inter alia will enter into an agreement restructuring its relationship with EISL
and certain other companies within the Elan group (the "Master Agreement").

1.    UNDERTAKING NOT TO SELL SHARES
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1.1   Each of Monksland and EISL hereby severally, irrevocably and
      unconditionally undertakes, represents and warrants to and confirms and
      agrees with the Company that until October 1, 2003, such Shareholder shall
      not, except as set forth in clause 1.2 sell, transfer, charge, encumber,
      grant any options over or otherwise dispose of, or permit the sale,
      transfer, charging, encumbering, granting of any option over or other
      disposal of, all or any of the Ordinary Shares or Preference Shares listed
      in Schedule 1 hereto (the "Shares", which term shall include other shares
      of capital of the Company issued to, acquired by or purchased by the
      Shareholder after the date hereof and attributable to or derived from such
      Shares, including Ordinary Shares issued upon conversion of the Preference
      Shares listed on such Schedule 1) or any rights or interest therein.

1.2   Nothing in this Agreement shall prevent the Shareholder from -

      (a)   converting the Preference Shares listed on Schedule 1 into
            Ordinary Shares;

      (b)   selling up to 944,124 Ordinary Shares to Investors pursuant to
            the Share Purchase Agreement;

      (c)   including the Ordinary Shares held by the Shareholder in the
            Registration Statement; provided that the Shareholder is not
            permitted to sell Ordinary Shares so registered under such
            Registration Statement until October 1, 2003 or as permitted by
            clauses (d), (e) or (f) below; or

      (d)   subject to applicable securities laws, selling Ordinary Shares
            where (i) the purchaser enters into a written agreement with
            the Shareholder, whereby such purchaser represents and
            confirms its intention to hold such Ordinary Shares for a
            period ending not earlier than 30th September 2003 (and for
            the avoidance of doubt the Shareholder shall not be in breach
            of this Agreement by virtue of such purchaser disposing of
            such Ordinary Shares before 30th September 2003) and (ii) the
            per share sale price of such Ordinary Shares is not less than
            90% of the closing sale price of the Company's American
            Depositary Shares on Nasdaq for the five trading days
            immediately prior to the date of such sale;

      (e)   accepting or agreeing to accept any offer to all the holders of the
            Company's Ordinary Shares (or all such shareholders other than the
            offeror and/or any body corporate controlled by the offeror and/or
            any person acting in concert with the offeror as defined in the City
            Code on Takeovers and Mergers) to acquire the whole or any part of
            the issued ordinary share capital of the Company; or

      (f)   transferring any Shares to a subsidiary or holding company or any
            subsidiary of any holding company as such terms are defined in S.
            736 of the Companies Act 1985 so long as such subsidiary or holding
            company agrees to take such Shares on the same terms as held by the
            Shareholder, including the terms of this Agreement.

2.    REGISTRATION STATEMENT

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      The Company shall notify the Shareholder of the form and content of the
      Registration Statement a reasonable time prior to the filing thereof.

3.    UNDERTAKING BY THE COMPANY

      The Company hereby agrees to waive the requirement in clause 3.2 of the
      1999 Subscription Agreement that the Company be given 10 business days
      notice before the Preference Conversion Date (as such term is defined in
      the 1999 Subscription Agreement).

4.    MISCELLANEOUS

4.1   A waiver of any term, provision or condition of this Agreement shall be
      effective only if given in writing and signed by the waiving party and
      then only in the instance and for the purpose for which it is given. No
      failure or delay on the part of the Shareholder or the Company in
      exercising any right, power or privilege under this Agreement shall
      operate as a waiver thereof, nor shall any single or partial exercise of
      any such right, power or privilege preclude any other or further exercise
      thereof or the exercise of any other right, power or privilege. No
      provision of this Agreement may be amended or otherwise modified except by
      a writing duly signed by the party against whom such amendment or
      modification is sought to be enforced.

4.2   This Agreement, the Master Agreement and the documents exhibited hereto
      constitute the entire and only understanding between or amongst the
      Shareholder and the Company with respect to the subject matter hereof and
      supersedes all prior agreements and other understandings of any nature
      whatsoever, whether or not in writing, relating to the subject matter of
      this Agreement.

4.3   This Agreement shall be binding upon each party hereto, together with
      their successors and permitted assigns, provided that no party shall
      assign its rights under this Agreement without the prior written consent
      of the other parties hereto.

4.4   This Agreement may be entered into in any number of counterparts, all of
      which taken together shall constitute one and the same instrument. Any
      party may enter into this Agreement by signing any such counterpart. This
      Agreement may be executed by either party by the delivery by such party by
      facsimile of a copy of the signature page of this Agreement, duly executed
      by such party. Any copy of this Agreement so executed by facsimile shall
      be deemed to be an originally executed copy of this Agreement.

4.5   This Agreement (and any dispute, controversy, proceedings or claim of
      whatever nature arising out of or in any way relating to this Agreement or
      its formation) shall be governed by and construed in accordance with
      English law. Each of the parties to this Agreement irrevocably agrees that
      the courts of England shall have exclusive jurisdiction to hear and decide
      any suit, action or proceedings, and/or to settle any disputes, which may
      arise out

                                       3
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      of or in connection with this Agreement and, for these purposes, each
      party irrevocably submits to the jurisdiction of the courts of England.

4.6   The Contracts (Rights of Third Parties) Act 1999 shall not apply to this
      Agreement and no person other than the parties to this Agreement shall
      have any rights under it, nor shall it be enforceable under that Act by
      any person other than the parties to it.

4.7   Except as provided in or anticipated by this Agreement, each party shall
      at all times during the continuance of this Agreement use its respective
      best endeavours to keep the contents of this Agreement confidential and
      accordingly shall not disclose details of the contents of this Agreement
      to any other person other than on a confidential basis, it being
      acknowledged that the Company may disclose the existence and terms of this
      Agreement to the Investors in connection with the Private Placement.
      Subject to Clause 4.8, no announcement or public statement concerning the
      existence, subject matter or any term of this Agreement shall be made by
      or on behalf of any party hereto without the prior written approval of the
      other party (Elan Corp in the case of the Shareholders).

      The terms of any such announcement shall be agreed in good faith by the
      parties.

4.8   A party (the "Disclosing Party") will be entitled to make an announcement
      or public statement concerning the existence, subject matter or any term
      of this Agreement, or to disclose Confidential Information that the
      Disclosing Party is required to make or disclose pursuant to:

      4.8.1 a valid order of a court or Governmental Authority; or

      4.8.2 any other requirement of law, regulation or any securities market or
            stock exchange;

      provided that if the Disclosing Party becomes legally required to make
      such announcement, public statement or disclosure hereunder, the
      Disclosing Party shall give the other party or parties hereto prompt
      notice of such fact to enable the other party or parties hereto to seek a
      protective order or other appropriate remedy concerning any such
      announcement, public statement or disclosure.

      The Disclosing Party shall fully co-operate with the other party or
      parties hereto in connection with that other party's or parties' efforts
      to obtain any such order or other remedy.

      If any such order or other remedy does not fully preclude announcement,
      public statement or disclosure, the Disclosing Party shall make such
      announcement, public statement or disclosure only to the extent that the
      same is legally required.

4.9   Any notice to be given under this Agreement shall be sent in writing in
      English by registered or recorded delivery post, reputable overnight
      courier or fax to:

              EISL at

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              Elan International Services Ltd.
              102 St. James Court
              Flatts,
              Smiths FL04
              Bermuda

              Attention:  Secretary
              Fax:        +1 441 292 2224

              Monksland at

              Monksland Holdings B.V.
              Rivierstaete Office Building - 6th Floor
              Amsteldijk 166
              1079 LH Amsterdam
              The Netherlands

              Attention:  Pieter Bosse/Marielle Stijger
              Fax:        +31 20 642 3185

              with a copy in the case of each of EISL and Monksland (receipt of
              which shall not constitute notice) to:

              Elan Corporation, plc.
              Lincoln House
              Lincoln Place
              Dublin 2
              Ireland

              Attention:  Senior Vice President, Legal
              Fax:        +353 1 709 4124

              Amarin at

              7 Curzon Street
              London
              W1J 5HG
              England

              Attention:  General Counsel & Company Secretary
              Fax:        +44 20 7499 9004

      or to such other address(es) and fax numbers as may from time to time be
      notified by either party to the other hereunder.

                                        5
<PAGE>
      Any notice sent by mail shall be deemed to have been delivered within 7
      working days after despatch or delivery to the relevant courier and any
      notice sent by fax shall be deemed to have been delivered upon
      confirmation of receipt. Notice of change of address shall be effective
      upon receipt.

4.10  Amarin and the Shareholder shall each be responsible for one half of the
      stamp duty reserve tax payable on the transfer of the Shareholder's
      Ordinary Shares to the depositary. Amarin shall be responsible for any
      other fees, duty or taxes arising from the registration set out in the
      Registration Rights Agreement and/or the transfer of such Ordinary Shares
      to the depositary. Save as aforesaid, each party shall bear its own legal
      and other costs incurred in relation to preparing and concluding this
      Agreement.

IN WITNESS whereof this Agreement has been executed and delivered as a deed on
the date first above written.

                                        6
<PAGE>
EXECUTED and delivered as a deed    )
by AMARIN CORPORATION PLC           )
Acting by:                          )

                                    )
                          Director  )     /s/ Richard Stewart
                                    )
                         Secretary  )     /s/ Jonathan Lamb

The Common Seal of                  )
ELAN INTERNATIONAL                  )
SERVICES, LTD.                      )
was hereunto affixed in the         )
presence of:                        )

                             Director     /s/ Kevin Insley

                             Director     /s/ Michael Elias

SIGNED and delivered as a Deed      )
by                                  )     /s/ Pieter Bosse
                                    )
as attorney for                     )     /s/ Klass Van Blanken
MONKSLAND HOLDINGS BV               )
in the presence of:                 )

------------------------
Signature of witness

                                        7
<PAGE>
                                   SCHEDULE 1

                                     Shares

Shareholder                               Shares

Elan International Services Limited       2,529,819 Ordinary Shares, less
                                          such number of Ordinary Shares
                                          as may be sold to the Investors

Elan International Services Limited       2,000,000 Preference Shares,
                                          which are convertible into an
                                          equivalent number of Ordinary
                                          Shares

Monksland Holdings BV                     124,000 Ordinary Shares (54,000
                                          of which are represented by
                                          American Depositary Receipts),
                                          less such number of Ordinary
                                          Shares as may be sold to the
                                          Investors

                                        8
<PAGE>
                                   SCHEDULE 2

                          Preference Conversion Notice

To:   Amarin Corporation plc (the "COMPANY")

We hereby give notice of our desire to exercise our rights conferred on us as
holders of Preference Shares to convert Preference Shares to ordinary shares of
the Company (the "CONVERSION RIGHTS") on [ o ] January 2003 (the "PREFERENCE
CONVERSION DATE") immediately after closing of the Private Placement in respect
of 2,000,000 Preference Shares of Pound Sterling 1 each in accordance with the
rights attached to the Preference Shares.

It is anticipated that the Company will waive the requirements in clause 3.2 of
Part 1 of the Appendix to the Second Subscription Agreement.

We desire that 2,000,000 ordinary shares of Pound Sterling 1 each in the capital
of the Company to be allotted on such exercise of our Conversion Rights be
allotted to and registered in our name and hereby authorise the entry of our
name in the register of Members in respect thereof and the delivery of a
Certificate therefore to Elan International Services, Ltd. as soon as reasonably
practicable after the Preference Conversion Date.

We agree to accept all the fully paid ordinary share capital of the Company to
be allotted to us pursuant hereto subject to the Memorandum and Articles of
Association of the Company.

EXECUTED AS A DEED by ELAN INTERNATIONAL SERVICES, LTD.

Date: ___ January 2003

                                        9
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                                    EXHIBIT A

   [see attached form of Share Purchase Agreement between Shareholder and
                                 Investors]

                                       10
<PAGE>
                                    EXHIBIT B

 [see attached Amended Private Placement Memorandum dated 10 December 2002
                          and Letter referred to]

                                       11

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