Keir Starmer is set to announce he will resign if he is found to have breached Covid-19 rules at a gathering of campaign staff for a curry in Durham. The Labour leader is expected to make a statement at 4pm after pulling out of a keynote speech on Monday morning amid wrangling over the wording of the commitment. Labour MPs expressed fury at the chaos – with briefing lines produced by Labour HQ as late as Monday morning saying that Starmer was emphatically not considering the possibility that he would pledge to resign. One senior source said there were several people within Starmer’s team had argued hard that he should stake his leadership on having done nothing wrong – a move that would put pressure on Boris Johnson. Starmer pulled out of a speech at the Institute for Government, as he wrestled with how to respond to renewed pressure on him over the conduct of aides at the gathering in Durham, with some reported to have been drunk. Durham police have launched a new investigation into the event and Labour has insisted the takeaway was ordered only to feed campaign staff working into the night on the Hartlepool byelection. A leaked memo obtained by the Mail on Sunday has added fuel to the story, showing the decision to order a takeaway was pre-planned, which appeared to counter earlier claims it was decided on the night as “nowhere served food”. Labour has said the memo shows the food was part of the working day and not a separate social event. The growing pressure from the scandal has caused some despair among Labour MPs for preventing the party from capitalising on local election results and key airtime ahead of the Queen’s speech on Tuesday. “We’ve lost hugely valuable time to make our case for what we would be doing in government by cancelling this speech – all because Keir is yet again unable to be bold,” said one MP, who has counselled in favour of Starmer saying he would be prepared to resign. A series of formal requests for comment to Starmer’s office and Labour brought no response. Asked why Starmer had pulled out of an Institute for Government event on Monday, at which he would have faced media questions, the only comment was that “plans change”. Wes Streeting, the shadow education secretary, earlier said he did not know why the decision had been made to pull out of the event. “No idea,” he told BBC Radio 4’s Today programme. “And I didn’t ask before I came on because I just thought it was such a trivial issue. I do think the idea that Keir has been somehow ducking scrutiny on this is ludicrous, given he has been in front of the cameras repeatedly over the weekend.” Streeting said the memo was a “standard visit plan” for such campaigns. “I don’t think anything that I saw in the memo in the Mail contradicted anything that Keir Starmer has said,” Streeting said. Mary Foy, the Labour MP for City of Durham, in whose constituency office the meal was eaten, denied reports on Monday that some staff had been drunk. “These allegations about my staff are untrue,” she said in a statement. “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.” The universities minister, Michelle Donelan, told Sky News the fact Starmer was being investigated “smacks of sheer hypocrisy given the relentless focus he has placed on Partygate”. Asked if he should resign if fined, she said: “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.”