Magrath, who has been with Balfour for eight years, is one of the longest serving main board directors following the recent series of resignations and retirements.

It was announced this morning that he will stay with the contracting group as CFO until his successor has been found.

His planned departure means that the three top executive board directors will be replaced in the wake of Balfour’s string of profit warnings.

Leo Quinn of QinetiQ is due to start as new chief executive officer in 1 January 2015, replacing Andrew McNaughton, who resigned.

In September chairman Steve Marshall also announced he will quit once a replacement is found.

This leaves planning and development director Peter Zinckin, 61, as the last surviving executive main board director from the Ian Tyler era.

Balfour said it was now on the hunt to find a new finance chief and a further announcement will be made in due course.

Chairman Steve Marshall said: “Duncan has been our CFO for six years.

“He has shown huge personal commitment to Balfour Beatty, and particularly in the recent more challenging times, his contribution and his resolve under pressure has been unwavering.

“Following the completion of the Parsons Brinckerhoff disposal and the announcement of our new group CEO, Duncan will be seeking new career challenges in 2015.

“In the meantime, he will continue on the board as group CFO, and will remain as strongly committed to this role as he has always been.”