Nicola Sturgeon has thrown down the gauntlet to Theresa May for the second day running – insisting a fresh independence referendum must be “made in Scotland”.
The first minister also called into question the “not yet elected” prime minister’s authority.
And she maintained the Scottish Government had a “cast-iron mandate” to put the issue to the Scottish people again.
But Mrs May used her Commons statement on the EU Council to hit back, telling MPs that now was “not a moment to play politics or create uncertainty”.
The Tory leader also said the economic case for independence did not stack up, adding: “The single market that is most important to Scotland is the single market of the UK.”
As the Commons debated the issue, it emerged the Scottish Parliament will vote on the matter next Wednesday.
MSPs will spend two afternoons debating whether the first minister should be given permission to seek a Section 30 order from Westminster.
It is understood the prime minister will not seek to block a second referendum altogether if Holyrood backs one, but move to control the timetable to prevent it going ahead until after Brexit.
Ms Sturgeon confirmed on Monday the vote should take place between autumn next year and the spring of 2019.
But the UK’s exit is not likely to be complete until the end of that timescale at the earliest.
Amid speculation the UK Government’s permission could be conditional on the SNP gaining an absolute majority in the 2021 Scottish elections, the first minister went on the offensive.
Speaking after a meeting of her senior ministerial team, Ms Sturgeon said: “It should be up to the Scottish Parliament to determine the referendum’s timing, franchise and question.
“Scotland’s referendum should be built on the principles of democracy, mandate and precedent, all of which should be observed as we move to give the people of Scotland the choice the current political situation demands.
“There should be no strings attached, no blocking mechanisms applied and no Downing Street diktat – Scotland’s referendum must be made in Scotland.”
She added: “That was the exact description the UK Government themselves used ahead of the 2014 referendum and the same principle should apply now.”
The first minister also attacked Mrs May on social media, writing: “Trading mandates does not put the prime minister on strong ground”.
She said she had been elected first minister “on a clear manifesto commitment” regarding another poll, while the prime minister had “not yet (been) elected by anyone”.
Speaking in the Commons yesterday, Mrs May claimed her government had been “working closely” with the devolved administrations, including the Scottish Government, on preparations for Brexit.
She said: “This is not a moment to play politics or create uncertainty.
“It is a moment to bring our country together, to honour the will of the British people and to shape for them a better, brighter future and a better Britain.”
Meanwhile, Spain’s foreign minister, Alfonso Dastis, played down the chances of an independent Scotland being able to remain in the EU when the rest of the UK leaves the group.
Any prospective application to the EU can be vetoed by any member and Spain is nervous about its own internal separatist movements.