Paul Drechsler, previously chief executive of Wates and now the president of the CBI, warned UK contractors that if they cared about the outcome of the referendum, they should “do something about it”.

“That means make sure that people who work for you understand what it means for your business.”

He said construction leaders should spend the next week talking about the issue at “toolbox talks, site talks, talks in the office”.

He warned that if Brexit led to staff being laid off in two months’ time they would ask why they had not been warned beforehand.

Mr Drechsler also told contractors to be clear with their suppliers about what the consequences of a vote to leave would be.

“Your supply chain has to understand what it means for you.

“If your customer thinks it’s very important for them, it should be important for you if you care about your customers.”

He warned that the Brexit would cause a “very significant shock” to the UK economy.

“The last time that happened was in 2008/09 and on the surface it was quite a straightforward issue [a bank failing] but nobody ever understood what that would mean.

“What it meant was years of significant job losses for the UK construction industry.”

He said there was no upside in the short to medium term.

“I think for the construction industry it would be more of what we have just been through and some are still recovering from.

“That’s why people should be talking about it.”

In the event of a vote to leave the EU, the first area of construction to be hit would be the commercial sector, he said, followed by housebuilding as the economy lost confidence and public sector and infrastructure projects as tax receipts fell.

The UK construction industry was reliant on the free movement of labour from across Europe, he said, because it needed to access talent from its other 27 member countries. Projects such as the Olympics would not have been built on time without it, he added.