Rule 2.10 Announcement

Costain Group PLC("the Company")

Rule 2.10 Announcement

On 28 March 2013 the Company announced that an application had been made for the admission ("Admission") of 605,533 new ordinary shares of 50p each in the capital of the Company to the Official List of the UK Listing Authority and to trading on the London Stock Exchange's market for listed securities.

Admission has occurred, and, for the purposes of Rule 2.10 of the City Code on Takeovers and Mergers, the Company confirms that a total of 66,149,839 ordinary shares of 50p each in the capital of the Company are in issue.

The International Securities Identification Number for the Company's ordinary shares is GB00B64NSP76.

11 April 2013