THE SNP manifesto for the Holyrood 2016 election will not include a commitment to hold another independence referendum, senior party figures have told the Sunday Herald.

The lack of a manifesto commitment on a second referendum means the chance of a new vote to quit the UK in the next parliament, which runs to 2021, is now remote unless a dramatic event such as Britain pulling out of the EU occurs.

SNP sources confirmed that, for the first time since devolution in 1999, the SNP manifesto for the Holyrood election will not include a firm pledge to hold a referendum.

Instead, it is expected to repeat the First Minister’s argument from her October conference speech that it would be wrong to propose a new vote without strong and consistent evidence that significant numbers of No voters had changed their minds.

However, it will also say it would be wrong to categorically rule out a referendum, in case of a sudden shift in opinion, perhaps caused by a vote to leave the EU against Scotland’s wishes.

The non-committal approach is designed to keep the SNP’s options open.

But party sources confirmed it also means that, if the SNP wins again in May and Sturgeon does want a referendum, unlike in 2011, she will lack an electoral mandate to back up her case.

That would leave her asking David Cameron to grant a legally binding vote, something the Prime Minister is highly unlikely to do after almost losing in 2014.

Although the SNP could, in theory, proceed without Westminster’s consent, any “consultative referendum” would probably become tied up in legal challenges.

The 2014 referendum was held on a legally secure footing only because Westminster handed the necessary powers to Holyrood on a temporary basis via a so-called Section 30 Order. Those powers have now expired.

Jim Sillars, the former deputy leader of the SNP, said it was a “great pity” and a great obstacle to independence that there would be no mandate for a second referendum.

He said: “I don’t think the Cameron government would budge an inch. The claim would be: you didn’t ask for a mandate, therefore you don’t have a mandate, therefore there’s no need for us to respond to your request for one. We’d come up against a brick wall.”

He said his choice would be to seek a “floating mandate”, telling voters the SNP would definitely hold a second referendum if the country's circumstances changed substantially.

Professor John Curtice of Strathclyde University’s politics department said he doubted Cameron would grant a second referendum even if the SNP did have a clear mandate - as he had only granted the first one because he assumed the No side would romp home.

The close 55:45 result in 2014 meant the Prime Minister would not tempt fate twice, he said.

And with polls showing roughly 53:47 support for the Union for the last year, Sturgeon would also be extremely reluctant to call a second referendum.

He said: “If the SNP were to call a referendum tomorrow, they could not be confident of winning it at all.

“The problem for both sides is that the referendum has left Scotland split down the middle on this subject, which makes it very very difficult to resolve.

“On the one hand, the Unionists cannot be sure Scotland will remain in the Union. Scotland is now the most problematic part of the Union, much more problematic than Northern Ireland.

“But equally the SNP, although they can win election after election, are not in a position where they can be sure of winning a referendum. Both sides are caught on a sharp, even divide that leaves neither side with the confidence that their side of the political project can be delivered.”