The Prime Minister is “fit for office”, Scottish Conservative leader Douglas Ross has said amid continued criticism over parties in and around Downing Street during lockdown.

Boris Johnson has been under pressure in recent weeks after he – along with his wife Carrie Johnson and Chancellor Rishi Sunak – received a fine for one of the gatherings.

Mr Ross, who had previously called on the PM to quit before the Russian invasion of Ukraine, has backed Mr Johnson.

He had submitted a letter to the backbench 1922 Committee pushing for a vote of no confidence in the Prime Minister, but has since rescinded it.

Speaking to the Scotsman, Mr Ross was asked if the Prime Minister is fit for office.

He said: “Yes, because he is leading the UK response to this crisis at the moment.

“But that doesn’t in any way diminish what he did and the actions that have been taken by those who investigate it.

“He is fit for office to continue with what the UK Government have done, his Government has done, to help the people of Ukraine.

“That’s not just me saying it, that’s President (Volodymyr Zelensky) who singled out Boris Johnson as a Western leader who has provided some of the greatest support.

“That relationship I don’t believe should just be cut off because clearly President Zelensky and the people of Ukraine welcome the support they’ve had from the Prime Minister and the UK Government.”

Mr Ross also said he had not seen anything that would “change his mind” on the Prime Minister’s position.

“Would it have been credible for me to have kept my letter in if at the same time I was saying ‘we have to be united in standing with the people of Ukraine’, in the same way that Keir Starmer said as the conflict started now wasn’t the time to replace the Prime Minister,” he said.

“(SNP Westminster leader) Ian Blackford stood up in the House of Commons and called for unity. I agreed with them when they said that.

“I just haven’t seen anything to change my mind that has potentially changed theirs.”

Nicola Sturgeon said the Scottish Tory leader’s comments show a “lack of principle” and “consistency”.

During a campaign visit to Barrowfield Community Centre in Glasgow on Friday, the First Minister said Boris Johnson should have “resigned already”.

She said: “I don’t think he’s fit for office and it’s not that long ago that Douglas Ross said he wasn’t fit for office and he should resign.

“Douglas Ross doesn’t appear to be able to hold to one opinion for more than a couple of days at a time.

“It just shows, I think, a lack of real principle. A lack of real resolve and consistency, and these are things people will draw conclusions on about Douglas Ross, but I think people have already largely made up their minds about Boris Johnson and he is deeply unfit for office.

However, Ms Sturgeon said the problems with the Conservative Party span beyond Mr Johnson’s leadership.

Scottish Labour deputy leader Jackie Baillie said: “It is little wonder Douglas Ross’ colleagues think he is a political lightweight when he has so happily abandoned his principles in this humiliating climbdown.

“Anyone can see that Boris Johnson is not fit for office, and defending democracy in Ukraine is no excuse for abandoning it here.”