The call follows reports in Construction News today that workers have quit the project over health and safety concerns.

The publication claims that it has seen evidence of staff working upwards of 70-hour weeks on the £745 million project as well as a 200% increase in accidents over the course of the project’s first year after construction got underway in 2015.

In September, a worker on the Aberdeen bypass was taken to hospital with head injuries after a falling piece of timber cracked his hard hat apart and knocked him unconscious.

Another worker was left with cracked ribs, a liver tear and dislocated toes after being crushed by a half-tonne pipe at the Milltimber stretch of the site back in March 2017.

The latest revelations follow Richard Leonard raising working conditions on the flagship project with Nicola Sturgeon at First Minister’s questions earlier this year.

The Labour leader told parliament the party has evidence of umbrella companies charging workers up to £100 to access their wages.

Mr Leonard said: “These are extremely serious allegations which must be thoroughly investigated as a matter of urgency by the Scottish Government.

“This is supposed to be a flagship project for the Scottish government – and so should be founded on a gold standard of health and safety as well as the terms and conditions of workers on the project.

“I have previously raised concerns directly with Nicola Sturgeon about the treatment of workers on this project, and the Labour Party will keep up the pressure until we see a step change in the industry in general and this public project in particular.

“What is clear is that we need to seriously change how public money is handed out. That is why Labour has repeatedly called for a comprehensive review of procurement in Scotland. It should be a lever for the government and other public agencies to drive working conditions and wider economic benefits up. The highest health and safety standards must be enforced.”

Recently, Galliford Try, one of the contactors delivering the Aberdeen bypass alongside Balfour Beatty, indicated that the firm expects to face additional costs due to various delays on the project, some of which caused by the collapse of joint-venture partner Carillion at the start of the year.

A spokesman for Transport Scotland, the project’s client, said: “The health and safety of those working on all major infrastructure projects and the surrounding community is of the utmost importance to us. Although the responsibility for the health and safety of workers rests with the contractor, Aberdeen Roads Limited, we have been working with them to enhance health and safety standards across the site.

“The project operates a culture of openness and transparency and the workforce is encouraged to report any event or condition they consider to be unsafe. Over the past year, the contractor has reported steady improvements through various reporting mechanisms and we will continue to work with them as the construction of this project nears completion.”