A “clever legal wheeze” to try and push through a vote on Scottish independence without the UK Government’s agreement is doomed to failure, according to a world-renowned referendum expert.

Matt Qvortrup, professor of political science at Coventry University, said that although he believed the Scottish Government had the mandate to hold another constitutional ballot, it did not have the powers to force it through in the face of objections from Westminster.

The Sunday Times reported that First Minister Nicola Sturgeon believes she can get around a possible legal challenge by putting the question to the Scottish people in a different way from the 2014 referendum.

She is due to unveil a "routemap" about how she intends to hold a new vote in October next year in a statement to Holyrood by the end of this month.

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Responsibility for constitutional matters was reserved to Westminster when Holyrood was set up in 1999.

This means a court would probably strike out any attempt to simply rerun the last vote, when Scots were asked “Should Scotland be an independent country?” and 55 per cent said “No”.

However, a so-called advisory referendum, testing support for independence or asking voters if they believe the Scottish Government should begin independence negotiations with London, could be allowed, it was reported.

The First Minister has previously objected to alternatives to seeking a Section 30 order from the UK Government to transfer powers to Holyrood to put any vote beyond legal doubt arguing she wanted to make the country independent rather than simply hold a referendum.

In the aftermath of the EU referendum in 2016 and the refusal of the then PM Theresa May and her successor Boris Johnson to agree to Indyref2, Ms Sturgeon came under growing pressure from within her party to back an alternative 'Plan B' path to independence without the consent of the UK Government.

In her Brexit day speech in Edinburgh on January 31, 2019, the First Minister warned of the problems with this approach: "For me to pretend that there are shortcuts or clever wheezes that can magically overcome the obstacles we face would be to do the independence cause a disservice.

"My job instead is to offer a path that can deliver independence.

"To achieve independence, a referendum, whenever it happens - whether it is this year as I want, or after the next Scottish election – must be legal and legitimate. That is a simple fact.

"It must demonstrate clearly that there is majority support for independence. 

"And its legality must be beyond doubt. Otherwise the outcome, even if successful, would not be recognised by other countries."

But Professor Qvortrup said that the Scottish Government could not hold a referendum of any kind - whether advisory or consultative - because powers over the constitutional future of the Union were reserved to Westminster.

“Any decision of that nature would be met with a judicial review challenge,” he told The Times.

“It is very likely it would be shut down by any court. From a legal point of view it is very difficult to see how it would work because it is not within the rule of law.”

Professor Qvortrup, whose most recent book Referendums and Ethnic Conflict includes a chapter on Scotland, said that if any referendum did manage to get past the courts it would be so watered-down that it would be easily boycotted by opponents of independence.

Ciaran Martin, the UK government’s former constitution director who helped to agree the framework for the 2014 referendum, told The Sunday Times: “The talk in Edinburgh circles is of a clever legal wheeze where softer legislation is drafted.

"Perhaps instead of a ‘referendum on independence’, the bill is instead about something like asking the people of Scotland for a mandate to open independence negotiations with the UK. Something like this might stand a better chance in court, though experts are sceptical.”

Angus Robertson, the Scottish constitution secretary, did not deny the reports when asked about them yesterday.

However, he told the BBC that there was no reason why Scotland could not have a legal independence referendum, and said that the SNP would continue to push for a vote based on an agreement between London and Edinburgh as in 2014.

“Given we have precedent, and it worked and wasn’t complicated, and with mutual respect, it was something we could all agree on,” he said.

The Scottish Conservatives, Labour and the Lib Dems have said ministers should be focusing on other priorities amid the cost of living crisis and recovery from the pandemic.

However, yesterday Scottish Labour Alex Rowley backed a referendum if a third option of 'home rule' or 'devo max' could be put on the ballot paper as an alternative to independence and an unreformed Union.