Ian Blackford has called on Scottish Conservative MPs to help kick Boris Johnson out of Downing Street.
The SNP leader at Westminster claimed Douglas Ross had been made to look "utterly ridiculous" by his previous support for the Prime Minister.
Ross, who is an MP as well as leader of the Scottish Tories at Holyrood, previously called for Johnson to quit over PartyGate before performing a U-turn on the issue.
The Prime Minister faces a vote of no confidence among Tory members at Westminster later tonight - but Ross has yet to comment publicly on how he will vote.
Blackford claimed Johnson was "completely unfit to be Prime Minister and he should have been removed from office long ago".
The SNP MP added: "He has broken the law, lied to parliament and distracted the UK government from tackling the issues that matter, including the Tory cost of living crisis and the long-term damage caused by Brexit.
"Tory MPs must finally put the interests of the public first. They must vote Boris Johnson out and do it now.
"And there cannot be any more flip-flopping from Douglas Ross and the Scottish Tories.
"Ross has made himself and the Tory Holyrood group look utterly ridiculous, while the rest of the spineless Scottish Tory MPs have shown nothing but craven loyalty to Boris Johnson – it is way past time for all of them to finally do the right thing and vote him out of office.
"But for Scotland, the outcome of this vote will change very little. We will still have a Tory government we didn't vote for, imposing devastating policies we do not support.
"The only way to keep Scotland safe from Tory cuts, Brexit and Westminster control is to become an independent country and escape the broken Westminster system for good."
Tory MSPs Murdo Fraser and Jeremy Balfour have already broken ranks to call for Johnson to go.
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