United States-based investment group Cathexis has claimed victory in its takeover battle for control of international construction services group ISG.

Cathexis last month made an improved offer of 171p per share for ISG, whose UK business includes a regional base in Ipswich, having had an earlier 143p per share offer rejected by the ISG board.

Although ISG initially said the improved offer, worth around £84.6milllion, still undervalued the business it later recommended shareholders to accept, saying that the substantial minority stake built up by Cathexis, of around 48%, would make it difficult for the remaining shareholders to exercise control even in the event of the offer lapsing.

Cathexis, which is based in Houston, Texas, has been a signficant shareholder in ISG since 2012 and was the largest investor in a round of fundraising undertaken by ISG in March 2015.

It held a 29.5% stake in ISG immediately prior to launching its cash offer, which was made in response to a fall in the ISG share price.

William Harrison, chief executive of Cathexis, said: “Cathexis is a long-standing supportive shareholder in ISG. Under our stewardship, we believe the company has a strong future and we are very pleased to have completed the acquisition.”

Cathexis was advised on the takever by international investment bank Altium. Mr Harrison added: “Altium’s strategic and tactical advice, its management of the transaction and its knowledge and application of the Takeover Code were invaluable to us.”

ISG provides fit-out, refurbishment, engineering, design and project management services for clients world-wide and last year reported revenues of £1.6billion.

Its Ipswich business was originally part of the Jackson Group of companies built up by Ipswich businessman Frank Jackson, who died in 2004, and began in 1960 as FJ Construction when building activities where split off from the civil engineering business Roadworks, which Mr Jackson had formed in 1952.

FJ Construction was later renamed Jackson Building and then, following its acquisition, ISG Jackson, before the name of its founder was dropped in 2011 as part of a group-wide rebranding.

Roadworks was later renamed Jackson Civil Engineering and, having become a separate business through a management buy-out in 2004, it continues to operate under this identity, now being part of Suffolk-based One Group Construction.