Speaking as he left talks with UK counterparts in London, constitutional affairs secretary Michael Russell said the SNP was committed to voting down the Prime Minister’s draft deal.

“It’s an emergency for all the nations in these islands to stop this deal,” he said. “This deal is a disastrous deal.”

Mr Russell claimed David Mundell “knows the damage this will do to Scotland” and criticised the Scottish secretary for standing by the proposed withdrawal agreement, which is set to be signed off at an EU summit in Brussels on Sunday.

Picture: ADRIAN DENNIS / AFP)ADRIAN DENNIS/AFP/Getty Images

“It’s beyond belief and in those circumstances the first thing to do is to stop this deal,” the SNP minister said following the latest meeting of the joint ministerial council yesterday.

“It is not this deal or nothing. That’s nonsense that is being sold vigorously by some of the people in that meeting.”

Mr Russell said if the SNP was unable to stop the “unacceptable deal”, then a second Scottish independence referendum should follow, claiming there was no greater illustration for independence than Brexit.

“The wrong thing to happen here is for Theresa May to dig in, which she has already done, and just say she is the only one that has the answers,” he said. “She is not and it’s important to say that.

“If the unacceptable deal goes through – and I never predict these things – there will be substantial economic damage and then I’m happy to say we will have to say to the people of Scotland ‘make your choice’.”

Mr Mundell accused the Scottish Government of changing his position on a Brexit deal to pursue an “independence agenda”, after months of warnings from the SNP about the risks of leaving the EU without a deal. He insisted he was trying to get the best deal possible for Scotland and attacked the SNP for “backing no deal”, which he said was the worst possible outcome.

Mr Mundell said: “The big change today was after 14 meetings where he had previously said what a bad outcome no deal would be for Scotland and the UK, Mike Russell said today SNP MPs would be backing no deal. “I think it’s a very serious situation and it will be particularly when we get to the meaningful vote.

“I hope when we get to that point people won’t be playing politics and looking for what outcome is most likely to get us an independence referendum or what outcome is most likely to get us a general election.

“I hope they will think what is in the best interest of people, of jobs, of the economy of Scotland and the UK.”

Mr Mundell also appealed to his Scottish Tory colleagues to back the Prime Minister because “there isn’t some purist version of Brexit available”.

Several Scottish MPs from his own party have refused to back Mr Mundell’s position on the deal, saying they will wait for further assurances on the impact of plans for the Irish border on the Union and on the future of fisheries.

One Scottish Tory, the pro-Brexit Aberdeen South MP Ross Thomson, has said he will vote against the deal.

The Scottish secretary again indicated he could quit if the UK remains tied to EU fishing policies and quotas past December 2020.

Mr Mundell and the other 12 Scottish Conservative MPs wrote to the Prime Minister threatening mutiny if fishermen and women remain tied to the Common Fisheries Policy.

With the EU chief negotiator Michel Barnier suggesting the transition deal could be extended by two more years until 2022, Mr Mundell said that would be unacceptable.

“I’m very clear we can’t extend the period and include the Common Fisheries Policy in that extension,” he said. “I could not support that. I’m not playing into the resignation soap opera. What I’m focused on is outcomes.”

Mrs May was due to meet Scottish Conservative MPs and MSPs at Downing Street later for a reception to mark the 20th anniversary of the 1998 Scotland Act that set up the Scottish Parliament.

Fight to defeat Theresa May's Brexit deal a national '˜emergency', SNP says