A claim that Theresa May and Jeremy Corbyn have considered giving Holyrood a veto over Britain’s future trade policy as they began their crunch Brexit talks has been dismissed as total nonsense by Whitehall.

As senior figures from both the Government and Opposition sat down this morning to thrash out a Brexit compromise, both camps have blamed each other for putting forward the idea of a “devo-lock”.

The suggestion - reported by BuzzFeed and based it said on information from two Government sources - is that if a prime minister wanted to change Britain’s future relationship with the EU, say, to scrap any permanent customs union, then he or she would first have to get the agreement of the devolved parliaments and assemblies in Scotland, Wales and Northern Ireland.

It is thought this would reassure Labour that any future Brexiteer premier could not take Britain out of a customs union, which might have been agreed to by the current UK Parliament.

A Tory source close to the cross-party talks said: “It’s a Labour suggestion. They have leaked it deliberately. It’s a way of tying us in forever as there’s no assembly in Northern Ireland, so impossible to deliver. It was leaked before the talks even began today and did not form part of the discussion yesterday.”

However, a Labour source suggested it appeared to have been briefed by the Government “for their own purposes”. He added: “It’s not a Labour leak; that’s Government spin”.

The Scotland Office said the idea was “not true” but a senior Whitehall insider was more forthright. He told The Herald: “It's b******s. It would undermine the devolution settlement that people in Scotland support so strongly.”

Ahead of the 2016 EU referendum First Minister Nicola Sturgeon suggested there should be a "devo-lock" on any Brexit result ie that a UK withdrawal should have required the consent of Scotland, England, Wales and Northern Ireland.