Annual Financial Report

Costain Group PLC

2 April 2026

Notice of 2026 Annual General Meeting and

Annual Report and Accounts for the year ended 31 December 2025

Costain Group PLC (the Company) announces that its Annual General Meeting will be held on Thursday 14 May 2026 at 3.00pm at Investec Bank PLC, 30 Gresham Street, London, EC2V 7QP (2026 Annual General Meeting).

Notice of the 2026 Annual General Meeting (2026 AGM Notice) and a form of proxy, together with the Annual Report and Accounts for the year ended 31 December 2025 (2025 Annual Report), are being made available to shareholders from today.

The 2026 AGM Notice and 2025 Annual Report are also available on the Company's website at Home | Costain and have been submitted to the National Storage Mechanism, where they will shortly be available for inspection at National Storage Mechanism | FCA.

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 2026 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 AGM | Costain 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 AGM | Costain and, where appropriate, by RIS announcement.

Dividend Timetable:

Enquiries:

Notes to editors

Costain improves people's lives by creating connected, sustainable infrastructure that enables people and the planet to thrive. Through the delivery of predictable, best-in-class solutions across the transport, water, energy and defence markets, we are creating a sustainable future and securing a more prosperous, resilient and decarbonised UK.