Block listing Interim Review

Name of applicant:

Costain Group PLC ("the Company")

Name of scheme(s):

(a) The Company's employee savings related share option scheme;

(b) The Company's employee Sharesave Plan.

Period of return:

From:

01 July 2017

To:

31 December 2017

Balance of unallotted securities under scheme(s) from previous return:

(a) 14,639 under the Company's employee savings related share option scheme;

(b) 49,638 under The Company's employee Sharesave Plan.

Plus: The amount by which the block scheme(s) has been increased since the date of the last return (if any increase has been applied for):

(a) Nil under the Company's employee savings related share option scheme;

(b) 745,969 under The Company's employee Sharesave Plan.

Less: Number of securities issued/allotted under scheme(s) during period (see LR3.5.7G):

(a) Nil under the Company's employee savings related share option scheme;

(b) 702,223 under the Company's employee Sharesave Plan

Equals: Balance under scheme(s) not yet issued/allotted at end of period:

(a) 14,639 under the Company's employee savings related share option scheme;

(b) 93,384 under the Company's employee Sharesave Plan.

Name of contact:

Tracey Wood, Company Secretary

Telephone number of contact:

01628 842444

Enquiries:

Costain Group PLC

Tel: 01628 842444

Tracey Wood

Secretary

Instinctif Partners

Tel: 020 7457 2020

Mark Garraway

James Gray