Exhibit 21

                                                                  CONFORMED COPY
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                             IRREVOCABLE UNDERTAKING
                    (Ohsea Holdings Limited (the "Company"))

To:  WestLB Panmure
     Woolgate Exchange
     25 Basinghall Street
     London
     EC2V 5HA

     Nabarro Wells & Co. Limited
     Saddlers House
     Gutter Lane
     London
     EC2V 6HS

     Professional Staff plc
     Buckland House
     Waterside Drive
     Langley Business Park
     Slough
     Berkshire
     SL3 6EZ ("Target")

Dated: 15 April, 2003

Scheme of arrangement in relation to the Target

We understand that:

(a)  the Target intends to propose to its shareholders a scheme of arrangement
     under section 425 of the Companies Act 1985 (the "Scheme") as a consequence
     of which we will be able, together with the shares that we intend to
     acquire under the terms of a share exchange agreement, to acquire all of
     the issued share capital of the Target for cash at a price of $2.10 per
     share;

(b)  the Scheme will be on the terms and conditions to be set out in a press
     announcement of the Scheme (the "Press Announcement") in the form of the
     attached draft Press Announcement, together with such additional terms and
     conditions as may be required to comply with the rules of The City Code on
     Take-overs and Mergers (the "City Code") and any other applicable laws or
     regulations, including the NASD Rules;

(c)  other than in respect of all the ordinary shares owned or controlled by us,
     CS Services Limited and Andrew Dixey and some of the ordinary shares owned
     or controlled by Benjamin Blackden, the Scheme will extend to all the
     ordinary shares of 2 pence each in the Target ("Ordinary Shares") issued
     prior to the close of business on the business day preceding the date on
     which the Court confirms the capital reduction involved in the Scheme

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     (the "Relevant Time"), including any Ordinary Shares issued as a result of
     the exercise of options under the Target's Employee Share Option Scheme and
     the Target's Company Share Option Plan prior to the Relevant Time (together
     the "Share Schemes");

(d)  under or in connection with the Scheme, it is proposed that we:

     (i)  issue to Andrew Dixey shares in the Company in exchange for the 69,000
          Ordinary Shares held by him, issue to Benjamin Blackden and Sally
          Blackden (as joint holders) shares in the Company in exchange for
          400,000 of the 408,000 Ordinary Shares held by such persons and issue
          to Osborne Clarke Trustees Limited (as nominee for the trustees of the
          Blackden Personal Settlement) shares in the Company in exchange for
          300,000 of the 393,500 Ordinary Shares held by the trustees (the
          Ordinary Shares being exchanged by such persons being referred to as
          the "Exchange Shares", and the Exchange Shares together with the
          93,500 Ordinary Shares held by Osborne Clarke Trustees Limited and the
          8,000 Ordinary Shares held jointly by Benjamin Blackden and Sally
          Blackden which are to be cancelled pursuant to the Scheme, the "NI
          Shares");

     (ii) issue to CS Services Limited, a person connected with us, ordinary
          shares in the Company in exchange for the Ordinary Shares held by it;
          and

     (iii) pay to each other shareholder of the Target a cash amount of $2.10 in
          respect of each Ordinary Share held by such shareholder; and

(e)  the proposal of the Scheme is conditional on:

     (i)  the receipt by us of completed irrevocable undertakings (in forms
          acceptable to us):

          (A)  from Andrew Dixey and Benjamin Blackden (the "Non-Independent
               Directors") and their associated persons undertaking not to
               exercise the voting rights in respect of the NI Shares and the
               Ordinary Shares held by Christopher Blackden, Mary Blackden and
               Philippa Berry at the court meeting of the holders of the
               Ordinary Shares (the "Court Meeting") to be convened by the High
               Court in England and Wales (the "Court") and undertaking to be
               bound by the Scheme; and

          (B)  to vote in favour of the Scheme from each of the independent
               directors of the Target in respect of a total of not less than
               2,000 Ordinary Shares

          (for the purposes of this clause, a person is associated with a
          director if that director would have to notify the Target under
          section 324 or section 328 of the Companies Act 1985 of any sale of
          shares in the Target by that person);

     (ii) the release of the Press Announcement,

     but we may waive condition (i) above in whole or in part (and either
     conditionally or otherwise) if we so choose and all our obligations under
     this undertaking will lapse if the above conditions are not fulfilled (or,
     where permitted, waived by us) by 12.00 noon on 30 April, 2003 (or such
     later time or day as we may notify to the board of the Target).

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In consideration of the Target agreeing to propose the Scheme to the
shareholders of the Target, we undertake, agree and represent to and with the
Target in the following terms:

1.   We are the beneficial owner of one Ordinary Share (the "Share"), free from
     all liens, charges, encumbrances and restrictions whatsoever, and of all
     rights attaching to it.

2.   We have full power and authority (without the approval or consent of any
     other person) to exercise (or procure the exercise of) all the voting
     rights in respect of the Share at general and class meetings of the Target.

3.   We will not exercise the voting rights (or will procure that the voting
     rights are not exercised) in respect of the Share at the Court Meeting and,
     following approval of the Scheme by the Court Meeting, we will irrevocably
     instruct the appropriate firm of solicitors to instruct Counsel to attend
     the Court hearing of the petition to sanction the Scheme and to undertake
     to the Court on our behalf:

     (a)  to be bound by the Scheme in respect of the Share; and

     (b)  to be bound by the Scheme and to execute and do or procure to be
          executed and done all such documents, acts and things as may be
          necessary or desirable to be executed or done by us for the purpose of
          giving effect to the Scheme.

4.   Other than in respect of the ordinary resolution approving the arrangements
     with the Non-Independent Directors (in respect of which we undertake not to
     exercise such voting rights), we will (either personally or by proxy)
     exercise (or procure the exercise of) the voting rights in respect of the
     Share in favour of the resolution(s) to be proposed at the extraordinary
     general meeting of the Target (the "EGM") to be convened by the Target in
     connection with the Scheme and the associated reduction in the share
     capital of the Target, the cancellation of (pound)13,122,000 standing to
     the credit of the Target's share premium account and amendments to the
     Target's articles of association.

5.   Unless and until the Scheme becomes effective or lapses, we will not except
     pursuant to the Scheme:

     (a)  sell, transfer, charge, pledge or grant any option over or otherwise
          dispose the Share or any interest in the Share; or

     (b)  accept any offer in respect of the Share or any interest in the Share
          (whether it is conditional or unconditional and irrespective of the
          means by which it is to be implemented); or

     (c)  restrict or (in so far as it is within our power to do so) permit the
          creation of any restriction on the voting rights in respect of the
          Share.

6.   We understand that, in accordance with the City Code, this undertaking will
     be referred to in the Scheme and will be available for inspection until the
     Scheme becomes effective or lapses.

(A)  All our obligations under this undertaking will lapse if:

     (a)  the resolution(s) to be proposed at the Court Meeting (are) not passed
          by the requisite majority at the Court Meeting (or any adjournment
          thereof); or

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     (b)  the resolution(s) to be proposed at the EGM (are) not passed by the
          requisite majority at the EGM (or any adjournment thereof); or

     (c)  the Court refuses to sanction the Scheme or confirm the associated
          reduction in the share capital of the Target; or

     (d)  the Scheme does not become effective by 31 July, 2003 (or such later
          date as we and the Target may, with the consent of the Panel on
          Take-overs and Mergers, agree); or

     (e)  the Scheme Document has not been posted to shareholders by 13 May,
          2003.

(B)  Any time, date or period mentioned in this undertaking may be extended by
     mutual agreement between the parties to this undertaking but as regards any
     time, date or period originally fixed or so extended time shall be of the
     essence.

(C)  References in this undertaking to a person having an "interest in shares"
     include all interests which that person would be required to notify to the
     Target if he were a director of the Target.

(D)  In this undertaking the expression the "Scheme" extends to the Scheme as
     modified from time to time.

(E)  This undertaking is governed by and shall be construed in accordance with
     English law.

IN WITNESS of which this undertaking has been executed as a deed and has been
delivered on the date which first appears on page 1.

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SIGNED as a deed            )                /s/    Andrew Wilson
by OHSEA HOLDINGS LIMITED   )                -----------------------------------
acting by:                  )                Name:  Andrew Wilson
and:                        )                Title: Director


                                             /s/    Stewart Harris
                                             -----------------------------------
                                             Name:  Stewart Harris
                                             Title: Director

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