Annual Information Update

Costain Group PLC("Costain" or the "Company")

Annual Information Update for the 12 months up to and including 30 March 2011.

1. RIS Announcements

The following UK regulatory announcements have been made via a Regulatory Information Service. A copy of these announcements can be obtained from the London Stock Exchange website, www.londonstockexchange.com/marketnews

Date Headline

2010

01.04.2010 Annual Information Update

12.04.2010 Annual Financial report

16.04.2010 Long Term Incentive Plan

20.04.2010 Deferred Share Bonus Plan

28.04.2010 SCRIP Dividend Preference Price

05.05.2010 Share Consolidation - updated timetable

06.05.2010 AGM and IMS

06.05.2010 Results of AGM

10.05.2010 Share Consolidation and Total Voting Rights

20.05.2010 Final Dividend

21.05.2010 Costain Skanska JV wins Crossrail Contract

24.05.2010 Costain wins ECI contract for Lancashire Council

30.06.2010 Trading update

09.08.2010 Costain wins Bond Street tube station contract

18.08.2010 Costain secures Lewisham BSF contract

25.08.2010 Half Yearly Report

29.09.2010 Nuclear Contract Award

01.10.2010 SCRIP Dividend Scheme

13.10.2010 Change of Advisor

14.10.2010 Document on Half Yearly results 2010

15.10.2010 Director/PDMR Shareholding

18.10.2010 Tunnel Contract Award

28.10.2010 The 2010 Interim Dividend - SCRIP alternative

08.11.2010 Interim Management Statement

29.11.2010 Contract update : AE&E Group GmbH and AE&E Inova AG

02.12.2010 AE&E Inova AG and the Belvedere facility

13.12.2010 AE&E Inova AG and the Belvedere facility

21.12.2010 AE&E Inova AG and the Belvedere facility

22.12.2010 Statement regarding approach to Mouchel

2011

04.01.2011 Costain wins Port Talbot highways contract

05.01.2011 Costain secures financial close on BSF contract

06.01.2011 Pre close trading update

06.01.2011 Revised approach to Mouchel Group Plc

06.01.2011 Statement regarding Mouchel's response to Costain

10.01.2011 Form 8 (OPD) (Costain Group PLC)

17.01.2011 Costain to build new bridge across Thames

18.01.2011 Costain awarded Highways contract

21.01.2011 Statement regarding revised approach to Mouchel

04.02.2011 Costain awarded airports contract

24.02.2011 Response to announcement by Mouchel Group plc

09.03.2011 Contract award Costain Skanska Joint Venture awarded third Crossrail contract

09.03.2011 Final Results

09.03.2011 Block listing application

2. Documents filed at Companies House

The Company has also made the following filings with Companies House. Copies of these documents can be obtained from Companies house, Crown Way, Cardiff, CF14 3UZ (by e-mail at [email protected] or, if you are a registered user, through Companies House Direct at www.direct.companieshouse.gov.uk ).

Date Description

2010

24.05.2010 SH02 - Consolidation

24.05.2010 Mem/Arts - Articles of Association

07.06.2010 AA - Group of Company's accounts made up to 31/12/2009

07.06.2010 CH01 - Director's change of Particulars Mr A Wyllie

22.06.2010 RES 01 - Alteration to Memorandum and Articles

2011

21.03.2011 AR01 - including latest statement of capital

30.03.2011 AA - Group of Companies accounts made up to 31/12/2010

3. Documents published and sent to shareholders

01.04.2010 Annual Report and Accounts 2009

06.09.2010 Interim Report and Accounts 2010

30.03.2011 Annual Report and Accounts 2010

Copies of information released can be obtained from the Company's Registered Office at:

Costain House

Vanwall Business Park

Maidenhead

Berkshire

SL6 4UB

28 April 2011

Enquiries: