Costain Group PLC (CSGQF) is a British engineering and construction company that provides smart infrastructure solutions across transportation, water, energy, and defence sectors in the United Kingdom. Founded in 1865 and headquartered at Seventh Floor, 70 St Mary Axe, London EC3A 8BE, the company operates through two main divisions—Natural Resources, encompassing water, energy, defence and nuclear energy; and Transportation, covering road, rail and integrated transport—and delivers services including advisory and concept development, specialist design, programme management, complex project delivery, technology integration, and asset optimisation. Its core offerings feature engineering and technology-led solutions for civil engineering projects such as roads and motorways (SIC 42110), other engineering activities (SIC 71129), and head office functions (SIC 70100), with notable involvement in major initiatives like HS2 lots S1 and S2, the Thames Barrier, Channel Tunnel, and ongoing nuclear and hydrogen projects.
Recent developments include a three-year multimillion-pound engineering contract with INEOS FPS for operations at the Kinneil Terminal in Scotland; a position on National Highways' technical engineering advice framework to enhance safety, reliability and decarbonisation; design work for Europe's first commercial-scale high-assay low-enriched uranium facility with Urenco and a pioneering underground hydrogen storage project; and a contract worth up to £1 billion with Sellafield Ltd for utility distribution systems refurbishment in a decommissioning programme.
In December 2025, Costain launched a £10m on-market share buyback programme following a pension scheme surplus valuation exceeding 101%; secured additional nuclear energy contracts with Urenco and Sizewell C, plus 260km of strategic pipeline work with Anglian Water through the Strategic Pipeline Alliance; and appointed Peter Mumford as managing director of natural resources. The company maintains a forward work position over four times annual revenue, with trading in line with FY25 expectations and strong bidding activity across sectors.