<PAGE>

                                                                   EXHIBIT 10.18

                             YORKSHIRE LINK LIMITED

                                       AND

                      MACQUARIE INFRASTRUCTURE (UK) LIMITED

                                       AND

                               BALFOUR BEATTY PLC

                      _____________________________________

                    AMENDED AND RESTATED SECONDMENT AGREEMENT

                      _____________________________________

                                       1

<PAGE>

                                                                  CONFORMED COPY

                              SECONDMENT AGREEMENT

THIS AGREEMENT is made on 26th March, 1996 as amended and restated on 30 April
2003 BETWEEN:

(1)      YORKSHIRE LINK LIMITED ("YLL") of (registered number 2999303) whose
         registered office is at Level 29 and 30, 1 Ropemaker Street, London
         EC2Y 9HD;

(2)      MACQUARIE INFRASTRUCTURE (UK) LIMITED ("MIUK") (registered number
         1540913) whose registered office is at Level 29 and 30, 1 Ropemaker
         Street, London EC2Y 9HD; and

(3)      BALFOUR BEATTY PLC ("BB") (registered number 395826) whose registered
         office is at 130 Wilton Road, London SWIV 1LQ.

WHEREAS:-

(A)      YLL has entered into an agreement on 26 March 1996 with the Secretary
         of State for Transport relating to the concession for the M1-Al Link
         Road (Lofthouse to Bramham) (the "CONCESSION AGREEMENT").

(B)      BB and Trafalgar House Services Limited ("THSL"), being an Affiliate of
         one of the original shareholders in YLHL, Trafalgar House Corporate
         Development Limited ("THCD"), agreed on 26 March 1996 to second or
         procure the secondment to YLL of personnel required by YLL from time to
         time to assist YLL in undertaking the M1-Al Link Road project (as
         defined in the Concession Agreement) and in particular in the
         performance of its obligations under the Concession Agreement
         ("ORIGINAL SECONDMENT AGREEMENT").

(C)      THSL was subsequently renamed Kvaerner Services Ltd ("KSL") and THCD
         was subsequently renamed Kvaerner Corporate Development Limited
         ("KCD").

(D)      In 1999, KCD was acquired by Macquarie European Infrastructure Plc and
         KCD changed its name to MIUK.

(E)      Under a deed of novation dated 3 February 2000 between YLL, KSL, BB and
         MIUK, KSL ceased to be a party to the Original Secondment Agreement and
         MIUK became a party in its place and various consequential amendments
         were made ("DEED OF NOVATION").

(F)      The parties now wish to amend and restate the Original Secondment
         Agreement as amended by the deed of novation on the terms hereinafter
         appearing. As the context may require, personnel seconded by MIUK to
         YLL shall hereinafter be called "THE MIUK PERSONNEL" and each and all
         personnel seconded by BB to YLL shall hereinafter be called "THE BB
         PERSONNEL" and the MIUK Personnel and BB Personnel shall together be
         called "THE PERSONNEL").

NOW IT IS HEREBY AGREED as follows:-

1.       SUPPLY OF PERSONNEL

1.1      Each of MIUK and BB shall use its reasonable endeavours to provide the
         MIUK Personnel or the BB Personnel (as appropriate) to YLL at such
         times and for such periods and either on a full or part time basis as
         may be required by YLL in its performance of the Concession Agreement.

1.2      The MIUK Personnel and the BB Personnel shall be deemed to be acting
         for and on behalf of YLL (to the extent that they would otherwise be
         acting for and on behalf of their respective employers in the
         performance of their normal duties) and shall at all times receive
         their instruction from YLL's Managing Director or his deputy. In the
         case of YLL's Managing Director he shall receive his instructions from
         the Board of YLL.

                                       2

<PAGE>

1.3      The MIUK Personnel and the BB Personnel shall be suitably qualified and
         professionally competent (the grades, numbers and individuals to be
         agreed between the parties). Except where otherwise agreed, each of
         MIUK and BB (as appropriate) shall provide YLL with details of their
         qualifications and experience.

1.4      MIUK and BB shall not change MIUK Personnel or BB Personnel seconded
         hereunder without prior consultation with YLL, provided that each of
         MIUK and BB reserves the right to replace MIUK Personnel and BB
         Personnel, as appropriate, with other suitably qualified and
         professionally competent MIUK Personnel or BB Personnel, as
         appropriate.

1.5      The MIUK Personnel and the BB Personnel to be seconded under this
         agreement on a full-time and part-time basis are to be agreed between
         the parties.

2.       PAYMENT

2.1      The fees payable by YLL in respect of the supply of the MIUK Personnel
         and the BB Personnel will be those set out in Part 2 of the Schedule
         hereto.

2.2      The fees shall be subject to any applicable VAT which, if applicable,
         shall be paid by YLL to MIUK or BB on each payment at the relevant rate
         in force from time to time.

2.3      Payments by YLL to MIUK or BB shall be made without any deductions or
         set-off.

3.       DURATION

3.1      The provision of the Personnel to YLL hereunder commenced with effect
         from the date hereof and shall continue for such period as YLL shall
         determine that the Personnel are required to be supplied to YLL in its
         performance of the Concession Agreement. YLL may terminate the
         requirement for any of the Personnel on not less than ninety days'
         notice.

3.2      In the event that YLL terminates the requirements for any of the
         Personnel pursuant to clause 3.1, YLL shall indemnify MIUK or BB (as
         appropriate) in respect of all costs, claims, liabilities or expenses
         arising therefrom suffered by MIUK or BB and relating only to the
         period of secondment hereunder.

3.3      Any party may terminate this Agreement by written notice to the others
         if any other party fails materially to observe or perform any of its
         obligations under this Agreement and has been notified in writing by
         the party aggrieved of the nature of the failure within fifteen days
         after its occurrence and has not taken steps to remedy such failure
         within thirty days after such notice.

4.       [NOT USED]

5.       [NOT USED]

6.       TRAVELLING AND HOTEL EXPENSES

         The Personnel shall be reimbursed their reasonable and proper
         travelling and hotel expenses incurred in the course of their
         secondment hereunder, in accordance with YLL's internal controls in
         force from time to time.

7.       ASSIGNMENT

         No obligations or rights arising under this Agreement may be assigned
         or sublet by any of the parties to any person or assumed by any
         successors thereto unless (i) such person is a company within either of
         the BB or Macquarie European Infrastructure Plc ("MEIP") groups of
         companies and (ii) the prior written consent of the other parties (such
         consent not to be unreasonably withheld or delayed) to such
         transaction, has been

                                       3

<PAGE>

         obtained. This Agreement shall enure to and be binding upon the
         respective permitted assignees, or successors of the parties hereto.

8.       LIABILITY

8.1      The liability of MIUK to YLL hereunder by reason of any breach of
         contract, tort or otherwise, shall under no circumstances exceed the
         aggregate of the fees paid by YLL to MIUK hereunder during the period
         of twelve months preceding the cause of action giving rise to such
         liability.

8.2      The liability of BB to YLL hereunder by reason of any breach of
         contract, tort or otherwise, shall under no circumstances exceed the
         aggregate of the fees paid by YLL to BB hereunder during the period of
         twelve months preceding the cause of action giving rise to such
         liability.

9.       CONFIDENTIALITY

9.1      During the period of this agreement and thereafter each party shall
         keep confidential and shall not disclose or transfer to or use on
         behalf of itself or for the benefit of any third party without the
         prior written consent of each other party any technical or confidential
         information or documentation of such other party obtained under or as a
         result of the implementation of this agreement, provided always that
         nothing in this clause is intended to prevent MEIP or BB or any of
         their subsidiaries or associates from time to time (subject always to
         the terms of the Concession Agreement) using any of the information
         knowledge and experience which any of them or their personnel shall
         have gained from their involvement in the M1-Al Link Road project or in
         any other similar scheme.

9.2      Upon the termination of this Agreement each party shall return to the
         other relevant party all documents belonging to one party and provided
         to any of the others in connection with the implementation of this
         agreement.

10.      NOTICES

         Notices shall be served upon any party to this agreement at its address
         referred to herein or at its last notified address and shall be deemed
         served ten days after posting if posted or two days after transmission
         if sent by facsimile transmission or if by hand on acknowledgement of
         receipt of delivery.

11.      LAW

         This agreement is governed by and shall be construed in accordance with
         English law.

COUNTERPARTS

12.      This agreement may be executed in any number of counterparts and by the
         several parties hereto on separate counterparts, each of which when so
         executed and delivered shall be an original, but all the counterparts
         shall together constitute one and the same instrument.

AS WITNESS the hands of the parties (or their duly authorised representatives)
on the date which first appears on page 1.

SIGNED by                       )
for and on behalf of            )     *
YORKSHIRE LINK LIMITED          )




SIGNED by                       )
for and on behalf of            )
MACQUARIE INFRASTRUCTURE        )     *
(UK) LIMITED                    )

                                       4

<PAGE>

SIGNED by                       )
for and on behalf of            )  *
BALFOUR BEATTY PLC              )




*    This agreement was restated and amended by an Omnibus Deed dated as of
     April 30, 2003 between Macquarie Infrastructure (UK) Limited, Macquarie
     Yorkshire Limited, Balfour Beatty plc, Yorkshire Link (Holdings) Limited,
     Yorkshire Link Limited, Kvaerner plc and Macquarie European Infrastructure
     plc, which was executed by the parties thereto as follows:


     MACQUARIE INFRASTRUCTURE (UK) LIMITED

     /s/ Colin Chanter
     Attorney

               Witness        /s/ Andrew Deszcz
                              Name:     Andrew Deszcz
                              Address:  65 Fleet Street, London


     MACQUARIE YORKSHIRE LIMITED
     /s/ Sean MacDonald
     Director

     /s/ Colin Chanter
     Director


     BALFOUR BEATTY PLC
     /s/ John Fox
     Attorney

          Witness             /s/ Andrew Deszcz
                              Name:     Andrew Deszcz
                              Address:  65 Fleet Street, London


     YORKSHIRE LINK (HOLDINGS) LIMITED
     /s/ John Fox
     Director

     /s/ Peter Dyer
     Director


     YORKSHIRE LINK LIMITED
     /s/ John Fox
     Director

     /s/ Peter Dyer
     Director


     KVAERNER PLC
     /s/ Nigel Williams
     Attorney

          Witness             /s/ Peter Dyer
                              Name:     Peter Dyer
                              Address:  14 Crofton Avenue, Chiswick
                                        London W4 3EW


     MACQUARIE EUROPEAN INFRASTRUCTURE PLC
     /s/ Peter Dyer
     Attorney

          Witness             /s/ Andrew Deszcz
                              Name:     Andrew Deszcz
                              Address:  65 Fleet Street, London