Balfour Beatty and Galliford Try’s consortium told the Scottish Parliament’s rural economy and connectivity committee on December 5 that the final 4.5 mile (7.5km) section between Parkhill and Craibstone would be open by Christmas.

The committee also heard that the £745 million project bill is now likely to reach more than £1 billion.

While 85% of the 36-mile bypass is now open, the River Don Crossing and the other unopened sections of road have continued to cause problems for the contractor.

Transport secretary Michael Matheson said ARL informed Transport Scotland of the latest missed deadline this week and warned that further payment will not be released without “critical” technical and commercial assurances.

Mr Matheson said: “This week, ARL informed us it was no longer able to meet its own deadline of concluding works at the Don Crossing before Christmas. This is just over a fortnight since it set this deadline publicly in Parliament. I have consistently urged caution and realism about ARL’s ambitious timescales. Unfortunately, as disappointing as this news is, it comes as no surprise to me it has been unable to achieve this.

“We have been here before with ARL. My officials and I will continue to work constructively and offer every assistance to get the remaining 4.5 miles open as soon as possible. I also want to pay tribute to the workforce who have undoubtedly been working hard during this most challenging time of year.

“It is well known that ARL has experienced a series of technical issues during the construction of the Don Crossing. In order for this Government to protect the public purse, it is imperative that ARL provides the necessary technical and commercial assurances for the Don Crossing. We cannot and will not contemplate releasing payments for this structure without these critical assurances.”

All work on the 36-mile AWPR was initially set to be completed by spring, but it was delayed to autumn, and then until December.

Mr Matheson added: “In terms of an opening date for this section, although ARL are forecasting January 2019, they have been unable to provide a definitive date.”