The firm, which employs around 50 staff, gives Costain front-end engineering capability and brings with it clients like Chevron and BG Group.

The deal offers some consolation after consulting engineer Mouchel rejected Costain’s £175m takeover bid last month – a move that would have transformed the contracting business at a stroke.

But Costain now looks set on a course of fulfilling its engineering design ambitions with a series of smaller bolt-on acquisitions.

Costain will merge the £4m turnover business into its energy and process division to give it a full design and build capability in the offshore and onshore energy market.

Andrew Wyllie, chief executive of Costain, said: “We are delighted to have acquired ClerkMaxwell. It is absolutely in-line with our strategy of broadening our existing front-end consultancy, project delivery and operations and maintenance offering through a combination of organic development and acquisitions.

“ClerkMaxwell is a fast growing business and will add complementary capabilities to our existing operations in the oil and gas sector, enhancing the full-service offering we can provide to our blue-chip customers.”

John Wilson, managing director of ClerkMaxwell, said: “We will bring additional skills and reach to an already strong oil and gas capability and Costain’s established customer base will provide a major opportunity for us to realise our ambition of becoming a market-leading provider of value adding, front end engineering services.”