POLLS suggesting four in 10 Scots think Nicola Sturgeon should step down just “run on constitutional lines”, Professor John Curtice has said.

The eminent polling expert, who serves as president of the British Polling Council, told The National that the First Minister’s popularity likely tracked support and opposition for Scottish independence.

He said that while Sturgeon had bucked the trend to hit highs in the ratings during the Covid pandemic, that boost in popularity had “now washed out”.

“So she’s back to where she was,” Curtice said. “She has half the country thinking she’s OK and half the country thinking she isn’t OK. That will run on constitutional lines.”

READ MORE: In-depth poll reveals Scots' views on de facto, EU, and independence referendums

The professor said it was hard to track progression of the First Minister’s rating because no polling firm had yet “really asked a question with a good time series”

“But probably we’re back to where we were, as far as Sturgeon’s popularity is concerned, back to where we were before Covid,” he added.

The comments undermine excited clamour from Unionists over the weekend after a poll found that 42% of Scots thought the First Minister should step down.

Less publicised was the finding that 45% of Scots thought she should stay on – with the split mirroring Scotland’s constitutional divide.

Among SNP voters in the 2019 General Election, just 15% said Sturgeon should resign as First Minister.

Kate Forbes, the finance secretary, was pointed to as a potential successor.

However, Forbes polled at just 7% when asked who should take over after Sturgeon, only narrowly beating John Swinney (6%) and Angus Robertson (5%). The fourth most popular choice was “other” (4%) but by far the biggest option was “don’t know”, which was chosen by 69% of people.

The lack of a clear successor and the support from within her party’s base suggests Sturgeon’s position is not at immediate risk.

Furthermore, a Lord Ashcroft Poll published on Monday found Sturgeon remained the most popular politician in Scotland.

However, Curtice questioned whether the First Minister had the same degree of control over her party’s “strategic direction” as she had in the past, pointing to the debate around the idea of a de facto independence referendum.

He said: “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.”

However, the polling guru noted: “This is nothing to do with public opinion, this is all to do with internal politics.”