BORIS Johnson’s biggest impact as Prime Minister has been as the “best recruiting sergeant ever” for independence, Scotland’s leading historian has said.

Professor Sir Tom Devine said it was impossible to think of any other prime minister in the last 100 years who has “sunk to the depths of Johnson’s mediocracy”.

His comments come after a week in which Johnson provoked fury after telling a meeting of Conservative MPs devolution was a “disaster” and “the biggest mistake” of Tony Blair.

The Prime Minister is also facing mounting criticism for standing by Home Secretary Priti Patel after an official inquiry concluded she had bullied staff.

Downing Street did not deny suggestions that Johnson had tried and failed to convince his standards ministerial adviser Sir Alex Allan to tone down his conclusion that her behaviour amounted to bullying as he found instances of shouting and swearing.

The adviser quit on Friday when the Prime Minister overruled his conclusion that Patel breached the ministerial code and stood by his Home Secretary.

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Following the election of Johnson last July, Devine wrote in an article in which he said most Scots regarded him as a “duplicitous buffoon who was totally unfit to hold the highest political office in the land”.

He told the Sunday National: “His performance since then has entirely confirmed that judgement beyond all reasonable doubt.

“It is impossible to think of any other prime minister in the last 100 years who has sunk to the depths of Johnson’s mediocrity.

“Indeed, the only function in which the self-styled ‘Minister for the Union’ has excelled has been in the role of best recruiting sergeant ever for the cause of Scottish independence.

“Hardly a day passes without his words or actions hastening erosion of support for the Union north of the Border.

“His decision not to sack Priti Patel as Home Secretary despite her being found guilty by the independent process of breaking the ministerial code will trigger righteous anger throughout the country.

“Not by any means for the first time a serious question of trust and integrity in high office hangs over Johnson.”

Last month a poll by JL Partners found Johnson’s unpopularity as leader was the biggest factor in a surge in support for independence, ahead of issues such as Brexit and the handling of the covid pandemic.

Another survey published in October revealed Nicola Sturgeon is more popular in England than Johnson, winning higher approval ratings in every English region except one.

However Devine said dislike of the Tory leader should not be the main driver of Scotland leaving the UK.

“The Scottish people should beware,” he said. “Their commitment to independence cannot be based wholly or even partly on the loathing of one politician  who will be consigned to the dustbin of history before too long.

“The future of the nation demands a mature discussion of the fundamental issues which confront the people of Scotland over the long term.

“The buffoon who happens to be  the present occupant of Downing Street is not one of them.”

Johnson’s comments on devolution sparked backlash on social media, including comments that it was the “last straw” in persuading people towards independence.

Fiona Duncan, 50, said she had been persuaded to join the SNP last year because of the current Tory Government and Brexit.

She said: “I think I have gone from 50% up to 100% independence.

“It was the arrogance of the Brexit vote, of there being no input from the devolved administrations about whether to have a Brexit vote and what the terms would be, what would happen if the countries diverged.

“It is just so blatantly unfair, there is no justice there and sense of respect for the devolved administrations.”

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She added: “I have never been a member of a political party before. I still trusted the fact the UK Government was a democratic organisation and everyone would get pretty much what they needed.

“But I don’t believe that as much as I did. And Boris Johnson in the past year is outrageously bad at the job, outrageously unsuitable for the job.

“He has destroyed any trust I had in the public to pick the right people.”

Jamie, 49, who did not want to give his last name, was against independence but said he joined the SNP earlier this year – with Brexit and Johnson among the factors in his decision.

He currently lives in South Warwickshire due to work, but is originally from Edinburgh and said he would move back to Scotland if he had the opportunity.

“In 2014 I was living in Dubai and I was against independence, largely because I had grown up with a very traditional Scottish Tory former landowning family that believed in the Union,” he said

“So in 2014 it seemed like trying to split up the family.

“If anything coming back to the UK and finding many who are effectively English nationalists has pushed me further towards Scottish nationalism.”

He added Johnson’s comments on devolution were “against the zeitgeist” and showed he “doesn’t understand Scotland”.