The delayed route saw results at both firms hit by a series of write-offs.

Balfour and Galliford confirmed today they has agreed a settlement with Transport Scotland which will seem them both receive £32m to cover additional costs on the job.

Galliford said: “The settlement brings to a conclusion a complex and challenging project, averting a lengthy and costly litigation process. 

“The settlement also removes a significant distraction and uncertainty, allowing the Construction business to focus on its core business, current and new projects which are expected to deliver improving margins, operating on multiple secured frameworks and in our chosen sectors.”

 The statement added: “Taken together with an adverse adjudication award on an unrelated historical contract in the period, the Group will report an exceptional write-off of circa £61m at 31 December 2019.

Balfour added: “Balfour Beatty continues to expect profit from operations for the year ended 31 December 2019 to be in line with the Trading Update provided on 12 December 2019.”

Costs on the £745m project rose to more than £1bn following delays which saw its full openening pushed back from Spring 2018 to February 2019.