Boris Johnson has stood down his backers as he failed to muster enough support to block a report into his Partygate lies.
The former PM was forced into a humiliating retreat as he told his cheerleaders not to vote against the damning findings.
MPs will decide on Monday whether to endorse the findings of the Privileges Committee that he deliberately misled Parliament over Partygate.
The Commons will debate its recommendation that Mr Johnson be banned from holding a parliamentary pass usually given to former MPs.
The Tories have designated it as a free vote meaning the party’s backbenchers can decide themselves whether to support or oppose if there is a vote, or choose to stay away altogether.
No10 has refused to say if Mr Sunak himself will take part.
Mr Johnson today was privately urging his supporters not to try and block the report, arguing the sanction has no practical effect.
He told them he was aware that he would get his pass back if re-elected as an MP.
But Tory sources suggested the former PM was actually trying to avoid holding a vote because he didn’t want to show how little support he had for him on the party’s backbenchers.
One said: “Nothing would more clearly show that his political career is over than just a tiny gang of true believers trooping through the voting lobbies to support him.”
If the report is not opposed then it could just be nodded through the Commons saving Mr Sunak from having to choose between further riling Mr Johnson by backing it, voting against the report and risking public anger, or avoiding the action altogether and facing allegations of being weak.
Senior Conservative MP Damian Green said abstaining from the vote to approve the damning report would not be rising to the occasion.
Asked if the PM must take part, the former de facto deputy prime minister told BBC Radio 4's Today programme: "Every individual will make up their own mind obviously. I think personally it's such an important act that deliberately abstaining is not really rising to the importance of the occasion."
He said if Mr Sunak does not take part it shows he is "the busiest", adding: "It's not for me to tell him how to behave in this sort of situation."
Mr Green said he intends to vote to approve the report with a "heavy heart".
In his first speech in Downing Street, Mr Sunak vowed to lead a government with “integrity, professionalism and accountability at every level”. But his first eight months as PM have been dominated by Tory sleaze rows.
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