Costain Regulatory News (COST)

Costain Group PLC(the "Company")

Notice of 2021 Annual General Meeting and

Annual Report and Accounts for the year ended 31 December 2020

Notice of the 2021 Annual General Meeting (the "2021 AGM Notice") and a form of proxy, together with the Annual Report and Accounts for the year ended 31 December 2020 (the "2020 Annual Report"), will be posted today to those shareholders who have elected to receive paper copies.

The 2021 AGM Notice and 2020 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.

At present, public health guidance and legislation issued by the UK Government in response to the COVID-19 pandemic mean that there remain restrictions on public gatherings and travel. We will therefore hold the 2021 Annual General Meeting ("AGM") at our offices at Costain House, Vanwall Business Park, Maidenhead, Berkshire SL6 4UB at 3.00pm on Thursday 6 May 2021 with the minimum attendance required to form a quorum and to conduct the business of the meeting. Shareholders will not be able to attend the AGM in person but can be represented by the chair of the meeting acting as their proxy. This is to comply with UK Government guidance and to protect the health and safety of our shareholders, colleagues and other stakeholders.

Shareholders will be able to watch the AGM via a live webcast. For details of how to register for the webcast, please visit our website at www.costain.com/agm from 30 April 2021. If you are unable to observe the webcast live, it will be available to view on-demand after the AGM.

The Board of Directors of the Company 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 or through CREST are set out in the 2021 AGM Notice. As mentioned above, given the current restrictions on attendance, shareholders are encouraged to appoint the chair of the meeting as their proxy rather than a named person who will not be able to attend the meeting.

The Board recognises the importance for our shareholders to make an informed vote and ask questions. Registered shareholders may therefore 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.

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.

1 April 2021

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