Support for Scottish independence is balanced on a knife edge with Yes and No voters split right down the middle, a polling expert has said.  

Speaking as Nicola Sturgeon prepared to Scotland’s launch an “updated independence prospectus” amid plans to hold a fresh referendum in 2023, Mark Diffley, Director of the polling firm The Diffley Partnership, said that support for either camp was “statistically a dead heat”.  

Mr Diffley believes that with no side taking a lead eight years after the last Scottish independence referendum, neither could be confident of victory should a fresh poll be held next year.  

However, with many people having already made up their minds, the chief battleground would be for the support of undecided voters, which could make up as much a 20 per cent of those taking part in the poll.  

Speaking to the BBC, he said: “A lot of water has gone under the bridge since 2014. If you look at the opinion polls now, there was one out a couple of weeks ago that showed Yes at 45% and No at 55% and there was a lot of commentary about ‘here we are, eight years on and nothing has changed’.  

“But actually a lot has changed. A lot has changed in the opinion polling. The average polling shows that we’re roughly around 50-50. The most recent poll shows exactly 50-50 for Yes and No. On average, this year, No is slightly ahead of yes but in the world of polling, it’s statistically a dead heat.  

“What that means is that if there were a campaign, which is by no means a formality, neither side would go in with any great confidence that it would win.” 

HeraldScotland:

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Speaking at the weekend, former First Minister Alex Salmond said that he expected support for independence to grow once the campaign was launched in earnest, as it had during the 2014 referendum.  

Eight years ago polling showed support for breaking up the UK to be around 35 per cent before the Yes campaign was launched, with the final vote showing that the prospect was backed by 45 per cent of voters.  

Mr Diffley said that a similar scenario could develop next time round, although the number of voters who could be convinced has shrunk.  

The pollster said: “He’s right to some extent. There are two issues here. If you look back at polling a year out from the 2014 referendum, there were polls that showed support for independence at around a third. 

“In the end, support for independence came in at 45 per cent, so he is right on one level at least to say that the campaign in 2014 really did change a lot of minds and made the final result closer.  

“However, the argument against that is that his time around I suspect that fewer of us are undecided … and this is borne out by polling. The most recent poll shows that only eight per cent are absolutely undecided on the Yes/No, whereas back then you were more likely to see 15-20 per cent of people undecided."

HeraldScotland:

Mr Diffley added: “So while the campaign did change a lot of minds last time, I think the evidence suggests it’s going to be harder to do so this time around.”  

However, Mr Diffley said that only that eight per cent were “absolutely” undecided, and that there could be as many as 20 per cent of voters who could be persuaded one way or the other.  

He said: “And they will be in play as a campaign comes into being. That’s fewer than it was in 2014, but around three quarters absolutely know how we will vote and the campaign won’t make any difference.”