Boris Johnson is facing another three potential fines for lockdown breaches, according to senior sources, as he suffered his first ministerial resignation over the Partygate scandal. In a sign of the continued nervousness in government that the prime minister’s position could come under threat when MPs return to Westminster from recess next week, a Downing Street source admitted the apparent lull felt like “calm before the potential storm”. Lords justice minister David Wolfson quit his role on Wednesday following the news that Johnson and Rishi Sunak had been given a fixed-penalty notice for breaking their own Covid laws by attending a party for the prime minister’s birthday in No 10. Wolfson said he was resigning not only because of the prime minister’s “own conduct” but also “the official response to what took place”. He said the behaviour stood in stark contrast to many in society who “complied with the rules at great personal cost, and others were fined or prosecuted for similar, and sometimes apparently more trivial, offences”. Johnson sought to rally senior ministers behind him by holding a virtual cabinet on Wednesday afternoon. The Welsh secretary, Simon Hart, said Johnson would not quit even if he received multiple fines. “I don’t necessarily see the difference between one or two,” he told Times Radio. By Wednesday afternoon, before Wolfson’s resignation, momentum appeared to have stalled for MPs prepared to oust Johnson – just two Tory MPs added their voices to calls for the prime minister to resign, the Amber Valley MP Nigel Mills and Craig Whittaker, the MP for Calder Valley. Mills said he would be writing a letter of no confidence to the chair of the 1922 Committee: “I think for a prime minister in office to be given a fine and accept it and pay it for breaking the laws that he introduced … is just an impossible position,” he said. In the Halifax Courier, Whittaker called for the PM to resign and “do the right thing” – though said he would not write a letter of no confidence, predicting that Johnson would win any vote. On social media, the majority of MPs rallied to Johnson’s defence. But a former No 10 adviser predicted the fines could still prove “fatal” for the prime minister’s career. “Conservatives, if they stand for anything, stand for the rule of law and the maintenance of order,” they said. “If they cannot abide their own rules, and do not show humility in the face of justice, it is impossible for them to maintain that mantle.” Key insiders said they believed Johnson was likely to receive at least three more fines for events that have not yet been fully investigated by police. The events that the Metropolitan police have yet to examine, which Johnson attended, include the May 2020 summer party, a November gathering in Johnson’s flat with his wife on the day of Dominic Cummings’ departure, and a leaving do for Lee Cain, a senior aide, in No 10 a day later. Sources said no attender had yet received a fine for those events. Some Tories have expressed concern that Johnson’s strategy has been to downplay the significance of the event for which he was fined – a short birthday gathering in the cabinet room. “It’s been a terrible comms blunder for MPs to be briefed that the event only lasted 10 minutes and that the PM has been unfairly maligned,” one Tory source said. Lord Frost, the former cabinet minister, also expressed concern that further damaging revelations were to come. “I think it’s not possible just to say, ‘That was then, this is now, let’s move on, the world is different,’ as the government is trying to this morning,” he told LBC. “We don’t yet know what other penalties may be issued, and to whom.” No 10 sources said the prime minister had attended the birthday gathering in the cabinet room in June 2020 for less than 10 minutes, eating salad from a plastic bowl and declining any alcohol or party food. But those who attended the birthday party for the prime minister say they have raised eyebrows at the description of the gathering, with one describing it as a “party atmosphere” with singing, attended by his wife, Carrie Johnson, and his interior designer Lulu Lytle. Another said they believe photos taken of the event by Johnson’s personal photographer – which have been disclosed to the official Sue Gray investigation into lockdown parties – would leave it beyond doubt that it was an event that breached the rules. One policing source said an assessment by Met detectives that the PM breached the rules more than once would increase future fines. The level of fine would go up each time Johnson was found to have, or accepted that he had, breached the rules he had introduced. The source added that the defence Johnson and his supporters were making, that people did not realise they were at parties, was “specious” because the raft of rules were written to stop any indoor gathering of people: “The law never talked about parties, it talked about gatherings. It does not have to be music and dancing – you could not gather indoors. “The whole reason was to stop the transmission of the disease. The disregard for public health is startling. Why would you not know you were breaching the rules?” Though three MPs who have previously called for Johnson to go said the war in Ukraine meant they did not believe it was the right moment for a contest, others stood by their letters of no confidence on Thursday, including Gary Streeter, Caroline Nokes, Anthony Mangnall and Tobias Ellwood. Another MP said they were deeply worried about further revelations and a “drip-drip” ahead of the local elections and the final Gray report. “Each one of these will come as a hammer into the nail of the Tory coffin and what the PM is doing is implicating all the MPs in this. We are in an a long, slow death march.” The chancellor, Rishi Sunak, has also apologised for breaching the rules, having received a fixed-penalty notice for attending the gathering, after a seven-hour deliberation during which he is reported to have been considering his position. Allies of Sunak said on Wednesday they believed it had been a missed opportunity for the chancellor not to resign on Tuesday after he receiving the fixed-penalty notice. “My view is he should have gone months ago and kept his integrity intact, but now he is at the mercy of potentially being sacked this summer,” one said.