Result of placing in Costain Group Plc

Further to the announcement released on 10th September 2024, ASGC Construction L.L.C. (the "Seller") announces that it has sold an aggregate of 41,666,666 ordinary shares of 1 pence each in the capital of the Company (the "Placing Shares") at a price of 91 pence per share (the "Placing Price") through a placing to institutional investors (the "Placing"). The Placing Shares represent approximately 14.97% of the Company's issued ordinary share capital. On the back of strong deal momentum, the Placing was upsized by approximately 39% from the original Placing size of 30 million ordinary shares (as announced 10 September 2024)

The aggregate gross sale proceeds raised through the Placing are approximately £37.9m.This represents a full exit by ASGC Construction L.L.C. of its position in the Company.

The Company is not party to the Placing and will not receive any proceeds from the Placing.

The proceeds of the Placing are payable in cash on usual settlement terms, and closing of the Placing is expected to occur on a T+2 basis on 13th September 2024, subject to the satisfaction or waiver of certain customary conditions.

Following its exit ASGC Construction L.L.C. will not be subject to the lock-up obligation announced on 10 September 2024.

Redburn (Europe) Limited ("Redburn Atlantic") is acting as sole bookrunner in connection with the Placing (the "Manager").

The Placing Shares rank pari passu in all respects with the Company's voting ordinary shares.