It is understood the visit late last week was prompted by spiraling cost overruns on the £373m smart motorway job and calls to the agency’s whistleblower hotline.

Costs on the project are understood to have soared by more than £100m, prompting concerns about the management of the scheme. This has forced Highways England to seek extra funding clearance for the project.

The 23-mile long smart motorway project is being delivered by Costain/ Galliford Try joint venture and has been running for over two years.  It was due to complete at the start of 2023, but sources say the job will run late into 2023.

A source told the Enquirer: “The Highways England investigation team were on the job for two days last week asking questions about subcontract awards.”

Highways England commercial programme director, Stephen Groves, said: “The M1 junctions 13 to 16 scheme is ongoing so cost figures aren’t yet finalised.

“We always scrutinise costs on any project and work closely with contractors to understand the reasons behind any increases.

“When matters are brought to our attention by way of our whistleblowing arrangements they are taken very seriously and always thoroughly investigated.”