Total Voting Rights

Costain Group PLC

(the 'Company')

1 October 2026

Total Voting Rights and Capital

In conformity with the Financial Conduct Authority's ("FCA") Disclosure Guidance and Transparency Rule 5.6.1(R) the Company notifies the market that:

As at 30 September 2026, the Company's issued share capital comprised 262,325,926 ordinary shares of 1 pence each, with each share carrying the right to one vote. The Company does not hold any ordinary shares in treasury. 

The figure of 262,325,926 shares may be used by shareholders as the denominator for the calculations by which they will determine if they are required to notify their interest in Costain, or a change to their interest in Costain, under the FCA's Disclosure Guidance and Transparency Rules.

The LEI reference for Costain Group PLC is 213800PKIJBZ2EDTKC88.

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