Ruth Davidson believes the Scottish Conservatives would have to break away from the UK party under a new name if Boris Johnson becomes Prime Minister, the Telegraph can disclose as the pair prepare to face off on Tuesday night in an EU referendum TV debate.

Senior sources close to the Scottish Tory leader said she thinks the former Mayor of London would be toxic to her party’s electoral hopes north of the Border if he succeeds David Cameron in the wake of a vote for Brexit on Thursday.

They said Ms Davidson predicts the Scottish Conservatives would have to “do a Murdo”, a reference to her former leadership rival Murdo Fraser’s controversial proposal to break away from the UK Tories and form a new right-wing party.

Although they did not specify the source of her antipathy towards Mr Johnson, she used an outspoken newspaper opinion piece to claim he had the same “brazen chauvinistic style” as Alex Salmond.