Michael Russell said “the clock is ticking” towards a constitutional deadlock unless the UK Government makes concessions over its plan for Brexit talks.
Scottish Government proposals to allow Scotland to stay in the European single market will be given detailed consideration by Whitehall officials, in a bid to keep talks alive.
But Mr Russell accused Theresa May of showing “contempt” for pro-EU voters in Scotland by rejected any plan that creates “internal barriers” to trade within the UK.
UK Brexit Secretary David Davis said the Scottish Government’s proposals were an “important contribution” but said ministers had yet to show they were practical or deliverable.
During First Minister’s Questions at the Scottish Parliament, Nicola Sturgeon said she was “determined to save Scotland from Brexit” by keeping it within the single market.
“It’s not just the case that the Tories are running towards Brexit, they want to drag Scotland kicking and screaming over that Brexit cliff-edge and I’m determined they are not going to get away with this,” she said.
Mrs Sturgeon said Scottish businesses were at risk of being “ripped out of the world’s biggest single market” because of the UK Government’s “obsession with immigration”.
Emerging from yesterday’s meeting of the Joint Ministerial Council (JMC) in London, Welsh Government ministers joined Mr Russell in accusing the UK Government of treating the intergovernmental forum on Brexit as a talking shop.
And there were claims that Sinn Fein, which is preparing to fight an election in Northern Ireland following the collapse of the power-sharing executive, could pull out of the process entirely.
Mr Russell said there was “Great frustration building up” about the lack of involvement in developing a common position on Brexit strategy ahead of the start of talks, which will be triggered by the invoking of Article 50 of the Lisbon Treaty by the end of March.
“There are difficult discussions, and they weren’t any easier today,” he said.
“The very strong concern remains, and it’s been heightened by today, that the process of getting this committee to agree a position is not going in the direction it should go.”
Mr Russell added: “Of course there’s a chance that it doesn’t agree a position. The clock is ticking.
“We would then be in a very serious situation indeed, where the promises from the prime minister would turn out to be worthless.”
Scottish Secretary David Mundell insisted talks were ongoing and that the Scottish Government’s plan would be examined.
He said: “If there is evidence that, for some reason, there should be a differentiated Scottish arrangement, then of course that will be properly looked at and considered.
“But at the moment I don’t have any evidence to suggest that Scotland would benefit from a differentiated arrangement from the rest of the UK.
“If we can get that access to the single market, without barriers and without tariffs, then that’s exactly what Scotland’s businesses are looking for.”
Asked what would happen if the parties failed to reach an agreement, Mr Russell said: “I’m going to come to the next meeting, I’m going to continue to discuss this, but I am even less hopeful than I was last time.
“We are not going to be put in a position where we walk away from this until we are absolutely sure, absolutely sure that nothing can be done.
“We’re patient, I just wish the UK government could show the goodwill and spirit of compromise that we’re showing.”