Transaction in Own Shares

Summary by AI ^BETAClose X

Costain Group PLC has purchased a total of 255,483 ordinary shares between May 27, 2026, and June 2, 2026, as part of its share buyback program, with weighted average prices ranging from 190.55 pence to 194.34 pence per share. These shares are intended for cancellation, and following their cancellation, the company's total number of ordinary shares in issue will be 267,078,540. The company has now acquired 2,677,495 shares in aggregate for cancellation under the program.

Disclaimer*

Costain Group PLC

03 June 2026

3 June 2026

Costain Group PLC

Transaction in own shares

Costain Group PLC ("Costain") announces that, in accordance with the terms of its share buyback programme (the "Programme") announced on 10 March 2026, it has purchased the following number of its ordinary shares of 1 pence each ("Ordinary Shares") on the London Stock Exchange through Panmure Liberum in the period from 27 May 2026 to 2 June 2026.

Date of Purchase	Number of ordinary shares purchased	Weighted average price per day (pence)	Highest price per share (pence)	Lowest price per share (pence)
27 May 2026	50,000	193.27	198.00	191.00
28 May 2026	41,500	191.77	193.40	190.80
29 May 2026	46,000	194.34	195.00	192.60
01 June 2026	45,000	190.55	193.00	187.80
02 June 2026	42,983	192.56	193.40	190.60

The Company intends to cancel the purchased shares. The Company does not hold any ordinary shares in treasury.

Costain has now purchased 2,677,495 Ordinary Shares in aggregate for cancellation under the Buyback Programme. Following settlement of the above purchases and cancellation of the purchased Ordinary Shares, the Group's total number of Ordinary Shares in issue will be 267,078,540 Ordinary Shares.

In accordance with Article 5(1)(b) of Market Abuse Regulation (EU) No 596/2014 (as it forms part of the law of the United Kingdom by virtue of the European Union (Withdrawal) Act 2018, as implemented, retained, amended, extended, re-enacted or otherwise given effect in the United Kingdom from 1 January 2021 and as amended or supplemented in the United Kingdom thereafter) a full breakdown of the individual trades made by Panmure Liberum on behalf of the Company as part of the Programme can be found at:

http://www.rns-pdf.londonstockexchange.com/rns/8486G_1-2026-6-3.pdf

Aggregate information:

Venue	Volume-weighted average price (pence per share)	Aggregated volume	Lowest price per share (pence per share)	Highest price per share (pence per share)
BATE	192.58	79,000	187.80	197.60
XLON	192.50	115,983	188.00	197.60
CHIX	192.56	21,000	188.40	197.60
TRQX	192.55	9,500	188.60	198.00

Enquiries:

Investors and analysts

Matt Jones, Costain

Matt.Jones@costain.com

+44 (0) 7860 922 341

Financial media - Headland

Andy Rivett-Carnac

Charlie Twigg

costain@headlandconsultancy.com

+44 (0) 7968 997365

+44 (0) 7946 494568

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