Checks are being carried out on the tax records and national insurance contributions of staff employed by firms such as Hochtief and Skanska, which are fully co-operating with the investigation.
The inquiry, which is being launched by the Rail Link Engineering consortium, a group that includes Bechtel, Arup and London & Continental Railways, is a response to political pressure from the construction unions.
A project insider said the client wanted to ensure that main contractors had checked that their subcontractors were not making bogus claims about their workers.
He said: “All contractors are feeling the pressure; main contractors because they do not want to upset the client, subcontractors because they know they could be booted off the scheme.”
Contractors were subject to intense criticism from unions and MPs for using bogusly self-employed labour on the first section of the project, which is due to be completed next year. The unions claimed that only one in four of the labour force was directly employed.
A spokesperson for RLE would not be drawn on the details of the audits, but confirmed that they were taking place.
She emphasised that it was a collaborative process, involving the unions. She said: “The issue of bogus self-employment is seen as an industry problem and we are working with contractors to ensure best practice is taking place.”
We are working with contractors to ensure best practice
Rail Link Engineering
Main contractors working on the project said they were aware of the clampdown and were fully committed to ensuring that all workers were directly employed.
A Hochtief spokesperson said: “Main contractors have joint bank accounts with the client and all accounts are fully accessible.”
A Skanska spokesperson added that it was working with the client, unions and subcontractors to ensure the workforce was directly employed.
The news of the investigation follows a union drive to stamp out bogus self-employment on government transport projects.
Officials from construction unions UCATT and the T&G have been holding regular meetings at the CTRL site with contractors and the RLE.
It is understood that union officials are now working with RLE’s audit department to ensure the checks are carried out fairly.