FIGHTING the next General Election as a de facto referendum is “perfectly legitimate” and opposition parties can’t prevent independence-supporting parties from doing it, the UK’s leading pollster has said.

“If they decide to fight an election on one issue, that is their choice,” said Professor John Curtice. “It is not for the opposition to say they can’t do it as it is their legitimate right. People can stand for election on anything they want to within the terms of the law.”

Speaking to the Sunday ­National following last week’s Supreme Court judgment that Holyrood ­cannot hold an independence referendum ­without Westminster approval, Curtice ­pointed out that voters in Scotland were already voting along ­constitutional lines.

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“The honest truth is that ­Nicola Sturgeon doesn’t need to say ­anything,” he said. “The opposition are right to say people could be voting on lots of things but they are not.

“If you look at what happened at the last Holyrood election, 89% of those people who say they would vote Yes in a referendum voted for the SNP or the Greens on the constituency vote and only 10% of people who say they are opposed to independence voted for the SNP.

“They are already virtually there and the point is that the constitutional question has become more and more important to our politics. If you go back to the SNP victory of 2011, that was won on the back of getting nearly 40% of the people who at that stage were opposed to independence voting for the SNP but those days are over. We have become polarised.”

Curtice said he was “surprised” the SNP had not “woken up” to this already, as the relationship ­between people’s attitudes towards the ­constitutional question and how they are voting in Scotland is stronger than the link between how people voted on Brexit in 2016 and how they voted in the 2019 General Election. Then, 75% of Leave voters voted for the Tories – who also won 20% of the Remain voters.

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Yet “nobody complains” that the Tories fought what was “arguably pretty close” to a single-issue ­campaign to “Get Brexit Done” and “nobody complains” when not only the Government but the opposition interpret the 2019 result as evidence that the public voted for Brexit.

“Actually, you can question that but nobody does,” said Curtice.

He added that it wasn’t obvious to him that the SNP would “do worse” as a result of deciding to make the constitutional question central.

“The electorate are already voting on constitutional lines,” he said.

It was also “not obvious” the ­Supreme Court decision would ­increase support for independence parties, even though a snap Channel 4 poll last week suggested it had.

“I am struggling to find the ­constituency of people who, until last week, opposed independence but who are thinking it is terrible that we can’t have a referendum,” said Curtice.

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“It is not obvious why the Supreme Court judgment should make an ­immediate difference. Any ­nationalist supporter has to understand that No voters do not share their view of the world. They don’t want a referendum because, to be honest, they probably think they might lose. They want to keep the Union, so until you persuade them otherwise they are unlikely to want a referendum.”

At the same time, “Unionists are wrong” when they say Yes voters don’t want a referendum, even though they might argue when it should be.

“Nicola Sturgeon is articulating the views of one half of the country but the other half, and this is the half she is trying to win over, are in a very different place, so it is not obvious to me why we should expect a dramatic change,” said Curtice.

While the court judgment might not have a direct effect on attitudes, he agreed it could be used as part of the argument over why Scotland should be independent and part of the vision of a more democratic country.

However, Curtice said Sturgeon (below) had set a “very high” target by stating that the vote for the independence parties in the next election would have to be over 50% but, if achieved, it would be “pretty hard evidence” of support for independence.

The National: First Minister Nicola Sturgeon

In order to achieve that target, the tactics would be the same as they would have been if the Supreme Court had said a referendum could be held next October – which would be to increase support for independence as it is “not yet high enough”.

“It is probably slightly less than the level of support for No at the moment, so you have got to get it up at least to the kinds of levels that found in the second half of 2020/early 2021 when you that series of polls where ­support was about 55.5% on average,” Curtice said.

Yet, even if over 50% of the vote is achieved, he said, it wasn’t clear that it would give the independence parties any more leverage at Westminster than if they only won 47% of the vote.

“But of course, if you are thinking long-term, the problem is how long you are going to be able to simply say ‘No’ without having ­consequences that you may not want – such as ­people becoming less compliant, or the SNP attempting to gum up the works at Westminster by not following Westminster convention,” he said.

“It is quite difficult to maintain certain constitutional arrangements if it is clear they no longer have majority support.”

Curtice also believes the biggest problem currently facing the SNP is rising support for Labour south of the Border – not last week’s Supreme Court decision.

Current trends show that although support for Labour in Scotland is at the expense of the Tories and may only result in a few more ­Scottish seats at the next General Election, Labour could still win an ­overall majority at Westminster, Curtice pointed out.

“The SNP would still dominate Scotland’s representation at Westminster,” he said. “But the problem is that the Labour Party now at least have the prospect of winning the ­General Election, even though they may not have much more than a handful of seats in Scotland. That is the really bad news for the SNP.

“The SNP were hoping for ­leverage – they wanted to be in the ­position after the next election whereby the only way you could form an ­administration at Westminster was with their acquiescence, and that therefore they would use that leverage to get a referendum out of Labour.”

Curtice added: “When we talk about the next General Election ­being a referendum on independence, the truth is the next General ­Election has always mattered because it ­potentially provided the opportunity of giving the SNP the kind of leverage they need in order to get a referendum out of somebody.”