Annual Financial Report

Costain Group PLC

8 April 2025

Notice of 2025 Annual General Meeting and

Annual Report and Accounts for the year ended 31 December 2024

Costain Group PLC (the Company) announces that its Annual General Meeting will be held on Thursday 15 May 2025 at 3.00pm on the Seventh Floor of 70 St Mary Axe, London, EC3A 8BE (2025 Annual General Meeting).

Notice of the 2025 Annual General Meeting (2025 AGM Notice) and a form of proxy, together with the Annual Report and Accounts for the year ended 31 December 2024 (2024 Annual Report), are being made available to shareholders from today.

The 2025 AGM Notice and 2024 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 of Directors is 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 electronically, by post, online through CREST or Proxymity are set out in the 2025 AGM Notice.

The Board recognises the importance for our shareholders to make an informed vote and ask questions. Registered shareholders may submit questions to the Directors in advance of the meeting by sending an email to [email protected]. 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.

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