Boris Johnson’s premiership was on the brink of collapse after the chancellor, the health secretary and a string of Conservative aides dramatically quit, dealing a crushing blow to his authority after a slew of self-inflicted scandals. Publishing damning resignation letters within minutes of each other, Rishi Sunak and Sajid Javid pointed to a lack of grip in Downing Street. The prime minister attempted to recover his authority by swiftly appointing Nadhim Zahawi as his chancellor and Steve Barclay as health secretary. But the credibility of the move was undermined as reports emerged that Zahawi had threatened to quit unless he got the job instead of the foreign secretary, Liz Truss, during a power struggle in No 10. In his resignation letter Sunak said the public expected government to be conducted “properly, competently and seriously”. Javid wrote: “We may not have always been popular but we have been competent in acting in the national interest. Sadly, in the current circumstances, the public are concluding that we are now neither.” He added: “The vote of confidence last month showed that a large number of our colleagues agree. It was a moment for humility, grip and new direction. I regret to say, however, that it is clear to me that this situation will not change under your leadership – and you have therefore lost my confidence too.” Sunak highlighted differences of opinion over economic management between him and Johnson in the run-up to a joint speech the pair had planned next week. It will increase speculation that he has not given up on a run at the premiership. Their resignations were followed by several more junior Tories quitting, including Alex Chalk as solicitor general, who said he could no longer “defend the culture and course set on [Johnson’s] watch”. Jonathan Gullis, a former ultra-loyalist, stepped down as a parliamentary private secretary, while Bim Afolami quit as vice-chair of the party. Gullis said: “I feel for too long we have been more focused on dealing with our reputational damage rather than delivering for the people of this country and spreading opportunity for all. It is for this reason I can no longer serve as part of your government.” The walkouts followed an extraordinary intervention over the Chris Pincher scandal. On Tuesday morning, former Foreign Office permanent secretary Simon McDonaldmade clear in an excoriating letter that Johnson had been briefed about an investigation into Pincher, the former deputy chief whip, in 2019. That contradicted statements from Downing Street that Johnson did not know about “specific” claims against Pincher before he quit last week amid allegations of drunken groping. During a febrile day in Westminster, MPs in the Commons were told Johnson “did not immediately recall” that he had been informed about an investigation into Pincher. The prime minister later conceded it had been a mistake to appoint Pincher as deputy chief whip, a role that involves pastoral care of MPs. “What I wanted was to give Chris Pincher, if not the benefit of the doubt, then the ability to prove that he could do better. And I’m afraid that he couldn’t. And I feel very, very bitterly disappointed and also sorry for the mistake I made,” Johnson said. Throughout the day, a growing number of Conservative MPs, including some who had previously been supportive, said this latest incident had been the last straw. Andrew Murrison, a Tory former minister, resigned as a trade envoy, saying: “Others must square, as best they can, their continuing enjoyment of your patronage with their personal sense of decency, honour and integrity but I no longer can … In February, reflecting on your achievements, I wrote a supportive op ed for the Guardian in which I said that if you were obliged to leave office you would do so with your head held high. I would no longer write in those terms.” Sunak published his resignation letter minutes after Javid, saying: “I am sad to be leaving government but I have reluctantly come to the conclusion we cannot continue like this.” He added: “The public rightly expect government to be conducted properly, competently and seriously. I recognise this may be my last ministerial job, but I believe these standards are worth fighting for and that is why I am resigning.” Afolami said: “I think what’s been very sad over the recent allegations about the former deputy chief whip and other things that have happened over the last few weeks is that I just don’t think the PM has any longer, not just my support but I don’t think the support of party, or indeed the country, any more. I think for that reason he should step down.” Johnson had earlier toured the House of Commons tea room hoping to shore up support among his backbenchers – but one MP said his message about the Pincher scandal had been “everyone deserves a second chance” – a sentiment that did not go down well with some present. As well as his new roles for Zahawi and Barclay, Johnson appointed the universities minister Michelle Donelan as education secretary to replace Zahawi. Sources close to other cabinet ministers, including Liz Truss, Ben Wallace, Dominic Raab and Priti Patel, said they would remain in post but rumours of more junior resignations continued to sweep through Westminster. The resignations of Javid and Sunak, both considered potential future leadership contenders, came at a moment of significant danger for the prime minister. Elections to the 1922 Committee executive next week are expected to strengthen the hand of rebels hoping to call another vote of no confidence. There is growing expectation among MPs that there will be moves to change the rules to allow a second confidence vote before the summer recess begins on 21 July, a feat previously seen as administratively impossible. MPs expect a full slate of Johnson’s critics to be elected to the committee next week, including Steve Baker and Andrew Bridgen. One MP who was sceptical about a rule change immediately said they had changed their mind over the weekend. Another MP said there were other solutions being discussed, including changing the rules so that if letters expressing no confidence reached a higher threshold – such as 25% of MPs rather than 15% – then a vote would be triggered immediately. The Labour leader, Keir Starmer, said: “If they [ministers] had a shred of integrity they would have gone months ago. The British public will not be fooled. The Tory party is corrupted and changing one man won’t fix that. Only a real change of government can give Britain the fresh start it needs.”