NICOLA Sturgeon’s resignation was “a reflection of the internal debate about independence in the SNP” rather than wider political rows about gender reform, polling expert Professor John Curtice has said.

Curtice, the president of the British Polling Council, said that the First Minister stepping down meant “the nationalist movement loses its best advocate”.

This was echoed by Ipsos Mori research director Keiran Pedley, who said Sturgeon's resignation would be "the biggest boost Unionism has had since winning in 2014".

READ MORE: Nicola Sturgeon quits as First Minister hinting at 'brutality of modern politics'

Curtice said that Sturgeon’s decision was “a reflection of the internal debate about independence in the SNP, rather than the gender recognition stuff”, according to Bloomberg.

“Certainly the next month will be about the internal debate in the nationalist movement about its strategic direction,” he added.

Speaking on Monday before the resignation, Curtice told The National: “It is clear that there is a fair amount of internal resistance inside the SNP to her strategy for a de facto referendum, and to that extent at least her ability to command the strategic direction of the party is perhaps in significant doubt for the first time since she became First Minister.”

Speaking at the press conference where she announced her resignation, Sturgeon said the decision on whether to treat the next General Election as a de facto referendum “must be taken by the SNP collectively, not by me alone”.

The National: First Minister of Scotland Nicola Sturgeon answers questions on Scottish Government issues, during a press conference at St Andrews House, Edinburgh. Picture date: Monday February 6, 2023..

She told journalists: “I know my party well enough to understand that my view as leader would carry enormous, probably decisive weight when our conference meets next month. I cannot in good conscience ask the party to choose an option based on my judgment whilst not being convinced that I would be there as a leader to see if through.

“By making my decision clear now I free the SNP to choose the path it believes to be the right one without worrying about the perceived implications for my leadership.”

Speaking to the BBC on Wednesday, Curtice said that Sturgeon “is still far and away the most popular leader in Scotland and her party is still dominant so far as the electorate is concerned”.

He went on: “That said however, her popularity is now shall we say as low as it has been at any point during her tenure as First Minister. She was very very popular in the early months and years. That reached a point where roughly half the people thought she was doing ok and half thought she wasn’t. She then got a very substantial boost during the pandemic when she was regarded as a very effective communicator and leader of her country, in contrast to Boris Johnson, but that’s been gradually diminishing.

The National:

“Of course, more recently … she’s hit some much choppier waters politically. But she’s still back in a position where roughly as many people think she’s doing ok and don’t think she’s doing ok. Not really the kind of levels where in itself would say well you’re now a big drag on your party and you need to resign.

“The honest truth is Nicola Sturgeon still is the most effective communicator for her party by far. There isn’t an obvious successor. Whether or not the party will be able to find somebody who is able to prosecute the case for independence as effectively as perhaps Ms Sturgeon might have been willing to do so if she were to carry on, that I think is still very much a big question.”

Pollster Mark Diffley said that voters “see no clear successor to the FM” which he said “illustrates how dominant a figure she has been for so long”.

"This makes it an open contest but suggests that whoever succeeds the FM has a huge job of gaining public recognition – in other words, she'll be a very tough act to follow,” Diffley added.