Scottish Secretary Alister Jack has said that any Scottish independence referendum without Westminster approval would be “illegal”.
The Conservative minister was speaking amid reports that the SNP could move to hold another vote on the nation’s future before the end of this year.
The legality issue has been raised following the SNP’s publication of an 11-point roadmap towards a second referendum.
The blueprint said that if the party was in government after the Holyrood election in May, it would request a Section 30 order from the UK Government to hold the vote, in the same way it did before the 2014 poll.
But it would also introduce and pass a Bill in the Scottish Parliament to begin making arrangements for the vote to be held, after the pandemic.
The Scottish Government would then challenge the Westminster administration to either grant the Section 30 order, or agree that Holyrood already has the powers to hold its own vote, or to try to block it in the courts.
Questioned about the document on the BBC on Sunday, Mr Jack said: “On that 11-point plan, which I’ve read – I mean, I don’t see 11 points in it, which is the first point I’d make.
“It seems quite muddled in its thinking. It says when the pandemic is over – well, that’s a view point.
“And it doesn’t make it clear at all whether it is a legal or an illegal referendum.”
I’m afraid the constitution is a reserved matter. It would be an illegal referendum, let’s be clear about that.”
On a vote without a Section 30 order, the Scottish secretary added: “I’m afraid the constitution is a reserved matter. It would be an illegal referendum, let’s be clear about that.”
The Sunday Times had earlier reported comments from an online discussion in which Constitution Secretary Michael Russell signalled that it was possible that a referendum could be held by Christmas.
He said it was “impossible to say” when it would be, but “best practice for referendums suggests that six months should expire between the legislation and the referendum”.
The newspaper said that the legislation could be passed in June, paving the way for a 2021 vote.
Appearing on Politics Scotland, Mr Jack also defended Prime Minister Boris Johnson’s visit north of the border last week, and said he was “keen for him to come back to Scotland as soon as possible”.
After critics claimed he should not have travelled while tight coronavirus restrictions were in place, Mr Jack said: “It is essential for the prime minister of the United Kingdom to get out around the United Kingdom and see what is happening on the front line in the fight against Covid.
“That is exactly what he did with the visits he was doing.
“You know, in any battle the general should go to the front line and hear from the people, those troops who are fighting, in this case the virus, exactly the issues they are facing. That’s why he is better informed.”
Mr Jack was also quizzed on UK Government plans to “bypass” Holyrood and deal directly with local bodies when it replaces EU structural funds with a new Shared Prosperity Fund.
He said: “This is the levelling up agenda. We want to improve transport links across the United Kingdom, especially up to the north of England and into Scotland and Northern Ireland.
“As happened with Europe, we want to show true devolution. We want the Highlands and islands and other regional authorities, who know exactly what is needed for the people they are closest to, to be able to bid for that money and be delivery partners with us.”