BRITAIN’S oldest conservative think-tank has called on David Mundell to resign as Secretary of State for Scotland.

The right-wing Bow Group say Mundell has purposely created a constitutional crisis to stymie Brexit.

A Scotland Office source said the claim was “bonkers”.

Founded in 1951, the Bow Group is one of Britain's oldest think-tanks, and has strong links to the Tories. Prominent alumni include Norman Tebbit, Michael Howard, Ann Widdecombe, John Redwood and Brexiteer Bill Cash. Former Prime Minister John Major even served as President.

The group have a strong pro-Brexit stance, and they believe Mundell is a secret undercover agent for Remain who has engineered a situation to make leaving the EU impossible.

Last night the group’s Scotland director, Jon Stanley said it was time for Mundell to go. He said the minister was responsible for creating a completely avoidable constitutional crisis.

And this, Stanley suggested, might have been on purpose.

“The law is clear that powers are devolved to Holyrood unless specifically reserved to Westminster and that such powers cannot be taken back without legislative consent from Holyrood.

“It is a flight of fantasy quite perverse to believe the Scottish Office and the Scottish Opposition in Holyrood are unaware of this or that they would risk the Scottish Government's proposed Continuity Bill to lock Brexit in the courts unless they in fact were keen for this to happen and for the Scottish Government to take the blame.”

He added: “This whole thing looks awfully like it has been a setup by David Mundell and Ruth Davidson to create a fight the SNP couldn´t resist that will lock Brexit in the courts.”

Mundell, he said, “should resign for having led his boss to a point where she could face a leadership challenge herself.”

“She certainly will if Brexit stalls,” the right winger warns, before adding: “There are plenty of MPs in Scotland now who could do a far better job. Some with a lot more integrity on Brexit.”

Scottish Brexit Secretary Michael Russell tweeted: “Blue on Blue....it may be a bizarre and fact-free take on events but it does indicate that the Tories are from being one big happy family.”

A Scotland Office source told The National: “The idea that the Secretary of State for Scotland and the leader of the Scottish Conservatives are plotting to thwart Brexit is completely bonkers. We are not treating this with any seriousness.”

A UK Government spokesperson said: “The EU (Withdrawal) Bill will provide consistency across the UK to ensure that all parts of the UK are ready for our departure from the EU. We are hopeful that we can reach agreement with the devolved administrations on the Bill in the coming weeks.”