While 85% of the giant scheme is now open, the final key stretch at the Don Crossing continues to torment the Aberdeen Roads Ltd consortium.

Now Scottish Transport Secretary Michael Matheson has warned that his office will not release any further payments for the structure until it has received firm commercial assurances.

Sources have revealed to the Enquirer that the bridge problems all come from movement with foundations early on in the project.

Delays and engineering problems have seen the £745m project fell behind schedule, with the expected cost now expected to be more than £1bn.

Last month Galliford Try revealed that its share of delays had cost it an extra £143m.

Contractors had pledged to open the final 4.5 mile section between Parkhill and Craibstone before Christmas.

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.”

He added: “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.

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

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.