Rishi Sunak has been told by a senior Tory MP not to dodge the vote on punishing Boris Johnson for lying to parliament.
Damian Green, the former de facto deputy prime minister, said abstaining would be “not really rising to the importance of the occasion”.
MPs will vote on Monday whether to approve the privileges committee report which found Johnson should have faced a 90-day suspension had he not already resigned and be banned from holding a pass to access parliament.
The sanctions proposed by the Tory-majority committee are expected to pass, with only a relatively small group of Johnson loyalists set to oppose the report’s findings, although many more Conservatives could simply not turn up.
Downing Street is yet to say whether the prime minister will vote on the report.
Speaking to BBC Radio 4′s Today programme, Green said he intends to vote to approve the report with a “heavy heart”.
Asked if it was important for Sunak to vote for it, he said: “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.”
Asked again how Sunak should vote, he said: “It’s not for me to tell him how to behave in this sort of situation.”
Jake Berry, a former Tory party chairman who is a close ally of Johnson, conceded he was “almost certain that Parliament will vote in favour” of the report.
But he told told ITV’s Good Morning Britain he will “certainly be one of those in the no lobby opposing this report, because I think both the conclusions and, to some extent, the way the committee was made up in terms of this report are wrong.”
The committee found Johnson deliberately misled the House with his partygate denials before being complicit in a campaign of abuse and intimidation against the MPs investigating him.
Branding him the first former prime minister to have ever lied to the Commons, the Privileges Committee said the offences merited a 90-day suspension which would have paved the way for a by-election if he had not preemptively resigned in protest.
Johnson was furious at what he called a “deranged conclusion”, claiming the 14-month investigation had delivered “what is intended to be the final knife-thrust in a protracted political assassination”.