Sir Keir Starmer said on Monday he will do the “right thing” and step down if he is fined by police for breaking Covid rules at Labour Party offices in Durham last year.
Speaking at party headquarters in London, the Labour leader said that he did not believe that the rules had been broken.
“I believe in honour, integrity and the principle that those who make the rules must follow them,” he said.
“And I believe those who undermine that principle undermine trust in politics, undermine democracy and undermine Britain.
“I simply had something to eat while working late in the evening, as any politician would do days before an election.”
The Labour leader also attacked his critics for seeking to “to feed cynicism to get the public to believe all politicians are the same” amid the so-called partygate scandal, which led to UK Prime Minister Boris Johnson and Chancellor Rishi Sunak being fined last month for breaking Covid rules.
“[The British public] deserve politicians who hold themselves to the highest standards and they deserve politicians who put the country first rather than themselves,” Sir Keir said.
“They will always get that from me.”
Labour says the meal under scrutiny was consumed between work events, meaning it was within the rules despite the ban on indoor socialising.
But the Labour leader was facing calls to answer fresh questions after a leaked memo suggested the meal was planned, with no further work apparently scheduled after dinner.
His deputy Angela Rayner issued a statement making a similar commitment, insisting she was at the event “working in my capacity as deputy leader and that no rules were broken”.
“Eating during a long day’s work was not against the rules. We have a prime minister who has been found to have broken the rules, lied about it and then been fined,” she said.
“If I were issued with a fine, I would do the decent thing and step down.”
Starmer accused of 'hypocrisy'
Having faced days of damaging headlines, Sir Keir was attempting to grab the initiative while putting pressure on Mr Johnson over his refusal to resign.
Government minister Chris Philp suggested Sir Keir could be “attempting to pressure the police into clearing him”, describing the move as “deeply inappropriate”.
The Tory MP was responding on Twitter to an ITV reporter saying an ally of the Labour leader said the move “puts some pressure on Durham Police who are being leant on in one direction”.
Conservative universities minister Michelle Donelan accused Sir Keir of hypocrisy, having pressured Mr Johnson to resign over partygate.
Asked if the Labour leader should resign if fined, she told Sky News: “I think this is a decision for him. He's going to have to search his soul after making this a top priority over the last few months at the expense of key issues like the rising cost of living, etc, but look, this is a decision for him.
“My takeaway is that it does smack of sheer hypocrisy.”
On Friday, Durham Constabulary said they had reversed an earlier decision on the case that no offence had been committed after receiving “significant new information”.
About 46 per cent of people believe Sir Keir should resign if he is fined by police, a YouGov survey of 1,674 adults showed.
This includes 48 per cent who voted Labour at the last election, which is higher than those who voted Tory, at 40 per cent.
With the police investigation continuing, 54 per cent responded that Sir Keir either probably or definitely broke the rules.
Labour MP Mary Foy denied reports that staff were drunk at the event, held in the City of Durham MP's constituency office.
In a statement, she said: “These allegations about my staff are untrue.
“I have already said that I and my team were working during a very busy period, including facilitating the leader's visit. I do not believe either I or my office staff broke any rules.”
Pressed on why Sir Keir pulled out of Monday's discussion, a Labour spokesman said: “Plans change.”
At the time of the Durham gathering, non-essential retail and outdoor venues including pub gardens were open, but social distancing rules — which included a ban on indoor mixing between households — remained in place.
Sir Keir previously said no restaurants or pubs were open at the time of the reported breach, so “if you didn't get a takeaway, then our team wasn't eating that evening”.
Labour has indicated that as Sir Keir was working, the meal did not constitute a social event.