POLLING expert John Curtice has suggested the "fractious" SNP leadership contest is ultimately to blame for the party’s slip in the polls.

Although there is evidence to suggest the arrests of former first minister Nicola Sturgeon and her husband Peter Murrell led to a downturn in the party’s fortunes, Curtice said the resignation of Sturgeon and her “relatively unpopular” replacement Humza Yousaf is what has caused voters to turn away from the SNP.

In a piece for Bylines Scotland, Curtice acknowledges a series of events have caused difficulties for the party, including the passage of the Gender Recognition Reform Bill – that saw several SNP MSPs rebel – and Labour’s rise in the polls following Liz Truss’s disastrous mini-Budget.

But he said the SNP leadership contest – which saw Yousaf battle it out against Kate Forbes and Ash Regan for the top party role – has been the “main culprit” behind the SNP’s shift in the polls.

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He said there has also been a weakening of the link between support for independence and backing for the SNP, with the loyalty of “natural” supporters having been “tested” by a change in leadership.

A year ago the SNP stood on average at 45% in the polls of voting intention for Westminster.

At the start of the contest, the SNP were at 43% in the polls of voting intention for Westminster, but by the end they had slipped to below 40%.

Once Yousaf was declared winner, support had slipped further to between 38% and 39%, in a bucking of the trend which usually sees a new leader giving an electoral boost to a party.

Curtice said that despite Sturgeon (below) suggestions it was her causing the party problems, Yousaf replacing her has actually made matters much worse.

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He wrote: “In announcing her resignation from the SNP, Sturgeon said that public attitudes towards her had become a barrier to her party’s progress and that of the wider pro-independence movement.

“While this was not the only stated reason for her resignation, her claim on this count at least has not been vindicated by events.

“For while public opinion was divided about her performance in office, for every voter who regarded her unfavourably at the time of her resignation, there was another who felt favourably towards her.

“Yousaf, in contrast, is relatively unpopular. There are nearly three people who feel unfavourably about him for every two that regard him favourably.”

Curtice added Yousaf’s unpopularity is not confined to Unionists with evidence suggesting a little less than half those who voted Yes in 2014 regard him favourably, while the figure for Sturgeon when she quit was 70%.

Support for the SNP slipped to 36% in the wake of Sturgeon’s arrest – and subsequent release – in connection with an investigation into the party’s finances which led to Labour “breathing down its neck”, but Curtice still maintains the leadership contest is largely to blame for the turning of the tide.

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He added that while Labour have benefitted from the fallout around Truss’s short-lived tenure as PM, their rise had no discernible impact on the SNP and was primarily at the expense of the Conservatives.

The other significant shift in the polls the SNP is having to grapple with is a weakening of the link between those who back independence and those that vote for the party.

Curtice wrote: “A year ago, the polls suggested on average that 48% of Scots would vote Yes in an immediate independence referendum. Despite everything in the last twelve months, that figure has not changed.

“However, whereas a year ago, 77% of those voted Yes in 2014 were backing the SNP, now the figure is just 64%.

“The last twelve months have tested the loyalty of the SNP’s ‘natural’ supporters. Above all it has been tested by the outcome of a change of leadership that leaves the party without the charisma at the top that was provided by [Alex] Salmond and Sturgeon.

“And even if the police investigation comes to nothing, internal divisions dissipate, and Labour begin to slip in the polls, that potentially crucial gap will still be there. But what, if anything, will the SNP be able to do to overcome it?”