Mark Diffley said that support for Scotland remaining in the UK was “absolutely in deadlock” with support for independence.
And he said it was unlikely that would change until a referendum campaign begins.
The polling expert told BBC Scotland’s The Sunday Show: “Everything will come down to the campaign – how good those campaigns are, how they speak to people, their positivity or negativity, so and so forth.
“That is what will really count.
“Because the polls are so tight at the moment, if we get into a campaign a marginal swing in either direction will make the different.”
His comments came after Scottish First Minister Nicola Sturgeon unveiled plans to hold a second independence referendum on 19 October 2023.
With Prime Minister Boris Johnson unlikely to agree to such a vote, the matter has now been referred to the UK Supreme Court, for a ruling on whether Holyrood can stage a referendum without Westminster’s consent.
Ms Sturgeon has already said that if she is barred from holding such a ballot, she will make the next UK general election – due to take place before the end of 2024 – a “de-facto referendum” on the issue.
A new poll, meanwhile, has showed 44% of Scots are opposed to another referendum, with 43% in favour.
The research by Panelbase for the Sunday Times also indicated that 48% would vote for independence, with 47% against, while 5% were undecided.
Ms Sturgeon hailed the results of that poll as “very encouraging”.
She tweeted that as well as Yes being ahead, there had been a “surge in support ” for Scots having a choice on independence in 2023, and also said the SNP was “within touching distance of majority of votes in GE should it become de facto #Indyref (which we hope isn’t necessary)”.
Mr Diffley, who founded the Diffley Partnership research company, said: “This poll puts support for independence slightly ahead of support for the Union.
"A poll during the week put support for the Union slightly ahead of support for independence.
“In my world, the world of statistics, what we have got is a statistical dead heat.
"We’ve got the two sides running at 50/50 on this, the country absolutely in deadlock and split down the middle.”
He added this situation was unlikely to change until the start of a referendum campaign, saying: “I suspect until we have a campaign it probably won’t move by a significant amount.”
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