Tory MPs who vote down an attempt to hold a parliamentary probe into partygate will be named and shamed by Labour.
The party vowed to launch an advertising blitz in the constituencies of Conservatives who back Boris Johnson.
It will form a key part of Labour’s campaign strategy during the local election campaign, party sources confirmed.
The plan emerged as Keir Starmer joined forces with the other opposition party leaders to try to force a privileges committee inquiry into claims the prime minister misled parliament when he said Covid rules were followed at all times in Downing Street.
MPs will vote on the proposal on Thursday - although the PM will miss the debate as he will be in India.
Starmer said: “We are urging Conservative MPs to do the right thing. To respect the sacrifices that their constituents made during the pandemic. To say that the public were right to follow the rules. And to vote in the national interest not under pressure from the party whips.
“The British public know that the rules were broken in Downing Street. Voting to say otherwise won’t persuade the public that everything was fine but will further damage the reputation of any Conservative MP who is happy to say it was one rule for the public and another for this government.
“Tomorrow’s vote is an important step to restoring decency, honesty and integrity into our politics.”
Labour sources later confirmed that they planned to launch advertising campaigns in the seats of Tories who vote against the parliamentary probe.
“We’ll be looking to ensure there is a price to pay for Conservative MPs who don’t support our motion,” said the source.
One senior Tory MPtold Radio 4′s World At One programme that he planned to abstain in tomorrow’s vote.
Sir Charles Walker, who is vice-chairman of the backbench 1922 Committee and a fierce critic of Covid lockdowns , said: “As much as I am deeply annoyed at what went on in No 10, I am also not in a position where I have much goodwill towards a Labour Party who, in my view, failed to advance any form of arguments or raise any of its own concerns about the consequences of a 20-month lockdown.”
He also warned that the prime minister’s position would come under threat if the partygate row rumbled on.
“If the fines keep racking up there is only so long that the Prime Minister will be able to lean on his party for supports,” he said.
“Ultimately it rests on the Sue Gray report and whether or not any more fines are issued,” he said.