THE SNP is so deeply divided it needs a period in opposition to “sort itself out”, one of the leading authorities on the party has said.

Professor James Mitchell also warned that unless Nicola Sturgeon delivered a big win for the SNP in May’s election, her authority was likely to be “short-lived”.

He said that after 14 years in power, fundamental splits over policy, independence strategy and Alex Salmond had led to the kind of “internal bloodletting” normally seen only after a major electoral defeat.

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The SNP’s divisions had gone “well beyond healthy debate” and risked undermining its performance in May and the chances of securing independence.

He said the party had “no credible strategy to deliver a referendum”, and had weakened its own cause with “intoxicated spin” over opinion polls and “empty rhetoric”.

He also said the SNP leadership had mishandled the debate on gender reform, and falsely painting critics as disloyal to the leader was “a sign of weakness”.

Opposition parties said the SNP focus on internal feuding was letting down the people of Scotland.

Prof Mitchell, Chair of Public Policy at Edinburgh University and author of a series of books on the SNP, its leaders and its rise to power, makes the devastating critique on the Sceptical Scot website.

He said the SNP’s divisions were deep and real, and could not be blamed on social media, or imagined differences between old and young members, or new members and veterans.

“Explanations need to  enter the more challenging areas of strategy and ideology,” he said, citing issues with independence, the economy and transgender rights.

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He said there was frustration at the party's perceived lack of progress in achieving independence.

He said: “There has also been no credible strategy to deliver a referendum.  

“The SNP ‘feeble fifty’ jibe when Labour’s 50 Scottish MPs (69%) failed to deliver devolution after the 1987 general election has come home to roost.  

“With 48 (81%) of Scotland’s 59 MPs, the SNP is unable to deliver a referendum.” 

He added: “Intoxicated spin of evidence from opinion polls has not helped.  

“Support has grown but far from the consistent and convincing lead that would be necessary to risk another referendum.  

“We hear less these days about the 60% that many members predicted lay just over the horizon.”

He suggested it was ironic that SNP Constitution Secretary Mike Russell recently quoted Canon Kenyon Wright of the 1990s Scottish Constitutional Convention saying that if the UK Government said No to a referendum “We say Yes and we are the people”.

Prof Mitchell said: “The SNP dismissed Wright’s empty rhetoric back in the days of the Constitutional Convention but the SNP’s ‘Plan B’ is no different.  

“Great rhetoric but without substance.”

He also said that, while the SNP had emphasised the “material change” brought about by Brexit, it had failed to address the changes it would mean for independence.

“There is a sense amongst many SNP activists that there has been little preparation or that the preparation has been poor.  Independence in Europe does not solve Scotland’s problems regarding free movement but only moves the problem.  Scotland faces a choice of losing free movement with European Union states or with the rest of the UK.”

Prof Mitchell also said the party and wider Yes movement were “split on currency as well as the economic and social prospectus of an independent Scotland”.

The recent conference decision to move to a separate currency “as soon as practicable” after a Yes vote had “resolved nothing and only led to fierce arguments on how soon is soon.”

Meanwhile the SNP Growth Commission had dismayed some members by moving the party to the right on the economy while failing in its aim of gathering support from business.

Prof Mitchell said Ms Sturgeon had also mishandled the debate on transgender rights.

Rather than opposition to gender reform coming from a “disaffected element out to undermine the leader”, he said there was “ample evidence” many of Ms Sturgeon’s own supporters disagreed with her on the issue.

He said: “Irreconcilable ethical principles arise in some areas of public policy and cannot be ‘solved’ but need to be negotiated.  Leaders need to take a stance but also need to emphasise where common ground exists and make an effort to reach out respectfully to those with whom they disagree. 

“Regardless of views on the issue, it is difficult to avoid the conclusion that the SNP leadership could have handled the transgender debate with greater sensitivity. Portraying those who disagree with a policy as disloyal to the leader is a sign of weakness.” 

On the breakdown in relations between Ms Sturgeon and her predecessor, he said Mr Salmond has been Ms Sturgeon’s “useful bogeyman in internal SNP politics just as Boris Johnston is her bogeyman in electoral politics”. 

However Mr Salmond, his political career over and his reputation in tatters, had “nothing to lose and the bogeyman has now become a real threat to Sturgeon”.

Mr Salmond is expected to tell a Holyrood inquiry under oath on Wednesday that Ms Sturgeon repeatedly mislead parliament and broke the ministerial code.

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Looking beyond May’s election, Prof Mitchell said the emergence of new Yes groups such as Now Scotland pointed to a power struggle over control of the movement.

He said: “The emergence of new organisations, notably Now Scotland, reflect concerns about the SNP’s direction under Nicola Sturgeon and a desire for more pluralism within the wider independence movement.  

“We are looking at a situation similar to the Brexit referendum when Leave UK and Vote Leave fought to become lead campaign organisation. 

“The SNP will remain firmly under Nicola Sturgeon’s control at least until May’s Holyrood elections but she will struggle to control the campaign for independence in any future referendum.

“What we are witnessing is the kind of internal bloodletting normally associated with the aftermath of a major defeat.  

“Much is a function of frustration and an inability to manage internal debate.  

“The SNP needs a period in opposition to sort itself out.  

“It has no credible roadmap to anywhere other than victory at the next Holyrood elections.  It hopes that a big win will restore Nicola Sturgeon’s authority.  

“If that happens, it is likely to be short lived.”

The SNP has been asked for comment.

Scottish Tory Chief Whip Miles Briggs said: “Everyone can see the deep divisions growing within the nationalist movement. The SNP are so divisive that they are now splitting apart their own party too.”

Liberal Democrat Scottish Affairs spokesperson Wendy Chamberlain MP said: "The SNP seem more concerned with brutal internal warfare than delivering for the people of Scotland.

"They are letting down the people of Scotland when the Government should be focused on putting the recovery first."

Labour MSP Neil Findlay said: “The SNP is riven with division from top to bottom. They are divided on tactics, policy and personalities.

“Such is the level of party infighting, we see a section of the party and some of its leading politicians cuddling up to vile figure that is [Wings Over Scotland blogger] Stuart Campbell, another group coalescing around the discredited figure of Alex Salmond, and another group trying to deny what even the dogs in the street know  - that Nicola Sturgeon misled parliament on several occasions.

“We are about to see a period of unprecedented political bloodletting – I wonder who will wake up with metaphorical horse’s head their bed?"