Company Announcements

Costain Group PLC

4 April 2023

Notice of 2023 Annual General Meeting and

Annual Report and Accounts for the year ended 31 December 2022

The Company announces that its Annual General Meeting will be held on Thursday 11 May 2023 at 3.00pm at No. 11 Cavendish Square, London, W1G 0AN (the "2023 Annual General Meeting").

Notice of the 2023 Annual General Meeting (the "2023 AGM Notice") and a form of proxy, together with the Annual Report and Accounts for the year ended 31 December 2022 (the "2022 Annual Report"), will be posted today to those shareholders who have elected to receive paper copies.

The 2023 AGM Notice and 2022 Annual Report are also available on the Company's website at www.costain.com and have been submitted to the National Storage Mechanism, where they will shortly be available for inspection at https://data.fca.org.uk/#/nsm/nationalstoragemechanism.

The Board is also keen to ensure that shareholders are able to exercise their right to participate in the meeting by voting. Details on how to submit a proxy vote by post, online, through CREST or Proxymity are set out in the 2023 AGM Notice.

The Board recognises the importance for our shareholders to make an informed vote and ask questions. Registered shareholders, whether they intend to attend the meeting or otherwise, may submit questions to the Directors in advance of the meeting by sending an email to AGM@costain.com. The Company will answer these in due course including, where possible and appropriate, by publishing the response on the website at www.costain.com/agm before the proxy voting deadline or by answering the relevant question at the meeting.

Any changes to the AGM will be communicated to shareholders before the meeting through our website at www.costain.com/agm and, where appropriate, by RIS announcement.

Enquiries

LEI: 213800PKIJBZ2EDTKC88