The SNP's heavy defeat at the Rutherglen and Hamilton West by-election will "embolden" rebels and weaken First Minister Humza Yousaf's authority over his party, according to the country's top expert on the SNP.

Professor James Mitchell, of Edinburgh University, gave his assessment on what the consequences of the devastating result would be for Mr Yousaf as he prepares to address his first annual conference as leader in Aberdeen next week.

The First Minister played a high profile role in the by-election, launching the party's campaign in August and talking regularly to voters on the doorstep with candidate Katy Loudon.

But Scottish Labour trounced their opponents winning 58% of votes cast with a 20% swing away from the SNP which took the seat in 2019 when Margaret Ferrier won the seat. She was removed as the MP in August by voters in a recall petition.

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Professor Mitchell told The Herald that Mr Yousaf’s authority was weak from the moment he won the SNP leadership back in March when he beat his nearest rival Kate Forbes by 52% to 48% in the second round of voting. The narrow win came despite most senior figures in the party endorsing his bid. Rows in the party have continued with long serving MSP Fergus Ewing last week suspended for voting against the government in a no confidence motion on the Green minister Lorna Slater in June

"What should have been an easy win, given the range of senior support he received and that he had advance notice that a contest would be held, his narrow margin meant his first task was to establish his authority," said Professor Mitchell.

"He went about this in a very strange way – first contrary to what he said in his victory speech he has governed as Team Humza, removing talent especially on the finance and the economy from his government, that he needed. 

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"The suspension of Fergus Ewing has proved a Pyrrhic victory – the leadership got what it wanted but a week’s suspension highlighted divisions and provoked a significant backbench revolt – though formally the vote was free, it was abundantly clear what the leadership wanted.  And once people get a taste for rebellion – especially if they feel excluded from decision making – they are likely to revolt again."

He added: "Rutherglen and Hamilton West further drains his already weakened authority.  We expected questions and challenges on the internal management and issues of party membership and finances at the SNP conference regardless of this result.  The question now is whether and the extent to which dissatisfaction and anger spills over onto the SNP conference floor.  His first party conference as leader will be very difficult.

"There is now a real prospect – though nothing is ever certain – that Labour will emerge as Scotland’s largest party next year and in the next Holyrood elections.  The morale boost for Labour is matched by damaged morale in the SNP."

Professor Mitchell continued: "Independence is not on the agenda any time soon as almost everyone knows – and even many in the SNP concede privately. 

READ MORE: SNP facing backlash over suspending Fergus Ewing

"The problem is the SNP outwardly behaves as if the next election will result in the start of negotiations for independence.  The formal debate at this conference in a resolution jointly proposed by Humza Yousaf and Stephen Flynn focuses on what would constitute a mandate – the problem is that this will simply make the SNP look as if it is talking to itself as a time when the public is focused on the cost of living crisis."

Mr Yousaf said on Friday the SNP should take its defeat in the Rutherglen and Hamilton by-election "on the chin".

Speaking to the PA news agency in Dundee, the First Minister said: "It's a tough day for the SNP, a disappointing result, there's no point pretending otherwise."

He said "a number of factors" were at play, including the "reckless actions" of former SNP MP Margaret Ferrier, whose breaking of Covid regulations led to her being kicked out of the party.

He added that the "collapse" of the Tory vote - with the party losing its deposit - and the subsequent shift to Labour, and the ongoing police investigation into the SNP's finances also had an impact.

But he added: "The SNP has to really take the result on the chin as well and understand there's a message that voters are sending to us too.

"We will reflect, regroup and we'll reorganise, and come back stronger."

SNP Westminster leader Stephen Flynn told BBC Radio Scotland on Friday morning that it cannot be "business as usual" within the party following the result.

Asked about Mr Flynn's comments, the First Minister said: "It's been obviously less than 12 hours since we got the result of the by-election.

"There'll be reflection that has to happen and has to happen with pace, so we'll do that.

"I think we need to make sure the party is a nimble and effective campaigning machine, and I think that's where the SNP is at its strongest.

"We also have to make sure our message is really crisp, really clear to people."

He said the party should utilise its "good track record" in government as well as highlight independence as being "key" to alleviating "some of the suffering of things like the Westminster cost-of-living crisis".

Asked if he bears any personal responsibility for the by-election defeat, Mr Yousaf said he has to "reflect", adding it "falls to me" to make sure the party is "ready and fit" for fighting a general election.

He underlined that he would take responsibility for the loss saying "the bucks stops" with him.

"The buck does absolutely stop me, but I think everybody knows this particular by-election had some very difficult contextual factors around it," he said.