Scrip Dividend Reference Price

Costain Group PLC

("Costain" or the "Company")

Scrip Dividend Reference Price

The Company announces that the Scrip Dividend Reference Price for the fully paid shares in the Company to be issued to shareholders who elect to receive the scrip dividend alternative for the final dividend for the year ended 31 December 2017 is 456 pence per ordinary share of 50 pence each.

The Scrip Dividend Reference Price has been calculated in the usual way as the average of the middle market quotations for the Company's shares as derived from the Daily Official List of the London Stock Exchange for the five business days commencing on the ex-dividend date. The Company's ordinary shares were marked ex-dividend on 12 April 2018.

Further Information:

Shareholders wishing to receive the scrip dividend in respect of the final dividend for the year ended 31 December 2017 and who have not already submitted a mandate form should return a mandate form to Equiniti Limited, Share Dividend Team, Aspect House, Spencer Road, Lancing, West Sussex BN99 6DA to arrive no later than 26 April 2018.

Mandate forms and the scrip dividend booklet containing the terms of the Company's scrip dividend scheme are set out on the Company's website at:

www.costain.com/investors/shareholder-centre/dividend-scrip/

If you have already completed a valid scrip dividend mandate form, it will remain valid until you cancel your election and you need not return any documentation to receive this scrip dividend.

Subject to approval at the Company's Annual General Meeting to be held on 08 May 2018, the final dividend for the year ended 31 December 2017, including the scrip dividend, will be paid on 18 May 2018 (the dividend payment date) to the ordinary shareholders of the Company on the register at close of business on 13 April 2018 (the record date).

For further information, please contact Equiniti on 0371 384 2270*.

 19 April 2018

*Lines are open 8.30am to 5.30pm, Monday to Friday, excluding bank holidays. If you are calling from outside the UK please telephone +44(0)121 415 7047.