The improved offer raises the valuation of Hyder by around £8m to £296m.

Arcadis also revealed today that it has just bought an extra 9.6% of Hyder’s total shareholding after striking a deal with one shareholder at the improved offer price.

The consultant now owns or has undertakings from shareholders for a 28% stake in Hyder.

A general meeting for shareholders will vote on the recommended offer on 25 September.

If the deal is approved, Hyder shares will suspend trading on the London stock exchange on 15 October, prior to the deal closing the following day.

The original offer from the Dutch firm in July was 650p a share, but this was trumped by Japanese rival Nippon Koei, forcing Arcadis to raise its offer to 730p late last month.

Nippon Koei has not ruled out returning with a better offer, but another bid looks unlikely now Arcadis owns a substantial stake in Hyder .

Arcadis has said the enlarged super-consultant would benefit from significant revenue and cost synergies, including savings through the use of global design excellence centres.

Hyder currently employs 4,000 staff globally while Arcadis has 22,000.

The deal shadows rival global consultancy AECOM’s acquisition of rival URS for £2.3bn last July.

A steering committee, jointly led by Ivor Catto, CEO of Hyder, and Stephan Ritter, Arcadis executive board member will detail how best to combine the two businesses.