Douglas Ross has tonight called for Boris Johnson to step down as Prime Minister.
The Scottish Conservatives leader said he would not back the PM at a vote of confidence on Monday evening.
Ross, who serves as both an MP and MSP, had previously argued that Tories should not try to remove Johnson because of the on-going war in Ukraine.
He has faced severe criticism from political opponents for changing his mind on the Prime Minister - with Lib Dem Willie Rennie claiming his party had "the backbone of a jellyfish".
In January, Ross and the vast majority of Scottish Conservative MSPs united to call for Johnson to leave Downing Street as a result of the PartyGate scandal.
But that position had changed by March - with Ross declaring the Prime Minister had regained his support.
But the PartyGate scandal did not die down in the weeks after his U-turn and Johnson was ultimately fined by the Metropolitan Police for his attendance at a lockdown-bursting party.
The Prime Minister's allies are confident he will win enough votes among Tory MPs to survive tonight's ballot at Westminster.
But the leader of the Scottish Conservatives will not be among his supporters.
In a statement, Ross said: "While war in Europe continues and the UK Government is providing such strong support to President Zelenskyy and the people of Ukraine, the timing of this vote is far from ideal.
"However, while I’ve not sought to bring this vote about at this time, it is now going ahead tonight, and I’ve had to consider how to vote on behalf of my constituents and the country.
"I do so knowing there are vocal opinions on both sides of this argument, an argument that has dominated much of the political discussion for many months.
"The Prime Minister can be proud of many of the successes his government have led on, particularly the Covid vaccine and the furlough scheme.
"However, I have heard loud and clear the anger at the breaking of Covid rules that we all did our best to follow, and even more so at the statements to Parliament from the Prime Minister on this topic.
Having listened closely to people in Moray who re-elected me to represent them, and from many people across Scotland, now that this confidence vote is upon us, I cannot in good faith support Boris Johnson.
"My vote tonight will support the motion of no confidence."
Scottish Labour leader Anas Sarwar said: "I’ve heard of politicians doing U-turns. This one does donuts."
To sign up to the Daily Record Politics newsletter, click here.
