Internal party polling and analysis shows victory for Mr Johnson in a leadership contest to succeed Theresa May would boost the Labour Party in Scotland, putting at risk several of the Westminster seats the Tories won in 2017 and making it impossible for Ruth Davidson to become First Minister.
“We’re going to do everything we can to stop that from happening,” a source said about the prospect of Mr Johnson getting the keys to 10 Downing Street.
It comes as the former foreign secretary, who resigned from the UK government and has mounted a guerilla campaign in the media against Mrs May’s plans for Brexit, prepares to mount his biggest challenge to the Prime Minister’s authority with a speech to a rally on the fringe of the Conservative Party conference in Birmingham.
The event today is expected to draw around 1,000 party activists and is timed to distract from Mrs May’s speech to conference tomorrow.
Organisers of the Scottish ‘stop Boris’ campaign hope the message his leadership could cost the party votes in Scotland – and damage hopes of winning a general election – reaches grassroots members across the UK.
Scottish Tory MPs are also being pressed to vote against Mr Johnson in the early stages of any leadership contest.
Internal party polling is understood to reflect the findings of a survey by former Tory peer Lord Ashcroft, which showed while Mrs May holds an eight-point lead in favourability ratings against Mr Corbyn, with 54 per cent preferring her as Prime Minister to 46 per cent for the Labour leader, Mr Johnson would find himself in a dead heat. Insiders say much of that lost support is in Scotland.
The former foreign secretary has come under sustained attack in Birmingham over his disloyalty, including from former allies in the Brexit campaign such as David Davis. Ruth Davidson also called for “a period of silence”.
Mr Johnson used a Sunday Times interview to describe Mrs May’s Brexit policy as “deranged” and “preposterous”. In remarks that have fuelled speculation about his leadership ambitions, he contrasted his position on Brexit with that of Mrs May, who backed Remain, saying: “Unlike the Prime Minister, I fought for this.”
Chancellor Philip Hammond launched a scathing attack yesterday, saying he does not expect the former foreign secretary to become Prime Minister.
Mr Hammond said “I don’t expect it to happen” and suggested Mr Johnson could not do “grown-up politics”.
He went on to attack the flamboyant Brexiteer for having “no grasp of detail” on complex subjects like Brexit, suggesting his greatest achievement to date had been introducing the “Boris Bike” cycle scheme while London mayor.
In his speech to conference yesterday, Mr Hammond predicted a “deal dividend” that could fund tax cuts and public service spending once a Brexit deal was reached. Mr Hammond’s forecast came as he called on Conservatives to stand “four square” behind the Prime Minister as she enters the final weeks of negotiations ahead of a hoped-for deal next month.
He also threatened internet giants like Google and Amazon with a new digital services tax to make sure they pay their fair share of the cost of public services.
“When the Prime Minister gets a deal agreed, there will be a boost to our economic growth,” Mr Hammond said.
“A ‘deal dividend’, which we will share in line with our balanced approach between keeping taxes low, supporting public services, reducing the deficit, and investing in Britain’s future.”
Mr Hammond said the Treasury was keeping sufficient “fiscal firepower” to hand to deal with any economic fallout from a no-deal Brexit.
But he urged Tories to unite to help Mrs May get a deal, saying: “Over the next few weeks we must stand together four square behind the PM.”