The five executive directors of Birse are likely to leave when Balfour Beatty completes its £32m purchase of the contractor.

A source close to the deal said: “The departures have not been determined, but that has always been the understanding between the two companies.”

However, the source said immediate redundancies among Birse’s 1200 staff were unlikely. The directors include chairman Peter Watson and managing director Martin Budden.

The takeover, the first in Balfour Beatty’s planned expansion drive, was announced at the start of last week. Negotiations are understood to have started six to seven weeks ago, but an offer document had been sent to shareholders by 30 June.

Many in the industry were surprised at the size of Balfour Beatty’s offer, owing to Birse’s historic liabilities. One financier is understood to have failed to find anyone to offer the market value of the company, which stood at about £26m before the Balfour deal.

In a trading statement last week, Balfour Beatty said its order book had grown to more than £8.5bn since the start of this year. It also spoke of its “determination to maintain its established growth momentum”. Further acquisitions of regional builders and civil engineering groups are expected to follow.