The launch of two new campaigns comes as subcontractors warn of widescale abuse of foreign workers.

One subcontracting boss said: “It’s not even being done subtly in London at the moment.

“I know a string of sites where you’ll see the same scenario play-out every Friday afternoon.

“The foreign workers gather near the gate then the Land Rovers arrive with the labour masters and their rolls of cash to hand out.

“The workers are getting paid way below average rates in cash while the labour firms bank the main contractor cheques.

“A lot of these workers are also put-up in accommodation organised by the labour firms who are exploiting them at every turn.

“And we’re not talking about small sites here – this is going on at some of the biggest jobs in London.”

The warnings come as a new report Operational Toolkit: Combatting Slavery in the Built Environment is released by the Supply Chain Sustainability School to support businesses with their modern slavery due diligence.

It warned: “The built environment is at a high risk of modern slavery and labour exploitation, due to ongoing challenges such as labour and skills shortages resulting in widespread use of temporary migrant labour, agency labour and subcontracts.

“Additional pressures from low profit margins and tight deadlines can result in businesses being more likely to ignore the usual protocols and processes for bringing workers onto sites.”

UK anti-slavery charity Unseen also released a video today to raise awareness of modern slavery on construction sites.

The charity worked with Berkeley Group, Laing O’Rourke, Skanska, Morgan Sindall, Kier, Galliford Try, VGC Group, Danny Sullivan, Randstad, Hays and Carmichael to produce the film below.