RUTH Davidson has admitted she would canvas on doorsteps for Boris Johnson if he succeeds Theresa May as prime Mminister.

The Scottish Conservative leader confirmed she would do so despite having been hugely critical of the former foreign secretary in the past.

The Scottish Tories even launched a secret campaign to stop Johnson becoming the new party leader.

It was code-named operation arse, one senior Tory source said, “so we’d all be clear who we were talking about.”

During an EU referendum debate at Wembley Arena in June 2016, Davidson also appeared to hit out at Johnson for “lying” about the cost of Brexit.

READ MORE: Nicola Sturgeon slams Ruth Davidson over support for Brexiteer

And an old tweet from Davidson’s account which criticises Johnson has been circulating online.

It was responding to an appearance by Johnson on the Andrew Marr show on March 6, 2016.

“Is it just me or is Boris floundering here?” she tweeted. “Not sure the bumble-bluster, kitten smirk, tangent-bombast routine is cutting through. #Marr”

However, in an interview with BBC Radio 4’s Today programme on Wednesday, the Scottish Tory leader said she would back Johnson if he becomes prime minister.

Asked if she thought Johnson would make a good prime minister, Davidson said she thought her preferred candidate Sajid Javid “would make a better one”.

She continued: “But I think that you can never tell how someone’s going to perform in the office of prime minister until they assume that office.

“It is so unique, it is so unlike anything else out there, that it’s very hard to say that past performance will give you an indication of what happens next.”

READ MORE: Ruth Davidson reacts to bombshell Tory poll on Brexit and independence

Asked whether she had U-turned on her opinion of Johnson, Davidson said: “Well I think that, um, er, I have challenged Boris Johnson, I’ve challenged lots of colleagues when I think they’ve merited challenging.

“I think in terms of the debates on Brexit, what I said, I didn’t call him a liar, I said that the people out there deserved the truth, and they did, and I stand by that.

“And if there’s something which I think deserves challenging, if he does end up in public office again, then I won’t realise from that, and I don’t think he would expect me too either.”

Interviewer Sarah Smith then asked the Scottish Tory leader if she could would canvas for Johnson ahead of a general election, telling voters that he is the best option for PM and whether she would expect voters to believe her.

Davidson replied: “Up against Jeremy Corbyn? Yes.”