Dominic Cummings left Downing Street after his relationship with the prime minister “fell off a cliff”, a former cabinet minister has said. Cummings left his role as chief adviser on Friday after a power struggle that has rocked the Boris Johnson administration just as Brexit talks head into a crucial phase next week, with London seeking a trade deal with Brussels before the end of the transition period on 31 December. The prime minister’s official spokesman insisted Johnson was not being distracted by the row and was “focused … on taking every possible step to get this country through the coronavirus pandemic”. The former Brexit secretary David Davis said Cummings’ “relationship with the prime minister fell off a cliff” and his departure was a chance to reset the government. And a senior Tory backbencher who supported Cummings over his coronavirus lockdown breaches said on Saturday he had been wrong to do so. Crispin Blunt said he should not have supported Cummings after his controversial trips to Durham and Barnard Castle at the height of England’s first lockdown were exposed by the Guardian and the Daily Mirror. Blunt said the lockdown journeys “stank”. Blunt was not one of the 45 backbenchers who called for Cummings to go at the time, but speaking on Times Radio he admitted the aide’s behaviour had “gravely undermined” the government’s message on coronavirus. Asked if he had been right to back the adviser, Blunt said: “With the benefit of hindsight, no. However, you’ve got to make a call about what is seen to be fair and proper in the circumstances, and Boris made a call on that.” During their visit to the north of England, Cummings drove with his wife and son to the picturesque town of Barnard Castle, 30 miles from his parents’ home, which he said was to check his eyesight was in good order. Blunt said that while he felt Cummings had done the “right thing for his family”, it had eroded public trust in the government and its messaging over the Covid crisis. “The politics of it obviously absolutely stank, and once it had been alighted upon by people it was a very bad example and it gravely undermined, obviously because of the huge attention it received, trust in the government’s policy,” he said. Davis said on Saturday that Johnson had been “very dependent” on Cummings for a long time, and called on the prime minister to “put right” the marginalisation of MPs over the past 11 months. “The whole attitude to parliament has been pushed, has been sidelined, and similarly, it is said, and I am not in a position to know, but it is said that cabinet has been sidelined too,” Davis told Times Radio. Davis said Cummings’ decision to leave his job through the front door of Downing Street, when his office was elsewhere in the building and there were several other exits, was “entirely deliberate” as he wanted to leave an “image”. He told BBC Breakfast: “He could have walked out the back door, which is almost sort of underground, not visible, or he could have walked out of the entrance out of Whitehall; out of the Cabinet Office – either would have been possible. “He chose to leave that image walking out with a box. He could have perfectly well put his coffee mug or whatever else was in it into his rucksack, but he didn’t.” Saturday’s papers were awash with claims and counterclaims over the events of the past 48 hours that led to the departure of both Cummings and the director of communications, Lee Cain, ending the grip of Vote Leave’s cabal on Downing Street. Cummings denied he was pushed, telling the Telegraph that stories that Johnson had held him responsible for negative briefings were “invented”. It reported that Johnson was unhappy with the characterisation of his partner, Carrie Symonds, in the media. He was “particularly riled by newspaper reports of Symonds being referred to by nicknames including ‘Princess Nut Nuts’ by Cummings loyalists”. A former special adviser to Grant Shapps, the transport secretary, told of the coercive and bullying nature of the Cummings and Cain operation, branding them a “schoolboy mafiosa” who had warned him that if leaks over coronavirus travel corridors didn’t stop “we are going to have to start shooting people”. Neil Tweedie, who was not found to have been responsible for any leak, said of Cummings and Cain in the Daily Mail that “fear was their tool”. “The Vote Leave mob, drunk on their success in the referendum and the election, believed they were untouchable,” he wrote. He told how Cummings, who demanded utter loyalty from special advisers to other ministers, held egotistical “spad school” Zoom meetings delivering monologues while “sitting at the end of the cabinet room table, the union flag draped behind him”. Others with knowledge of the inner workings of Downing Street came to Cummings’ defence on Saturday. One former Downing Street adviser told the Guardian Cummings’ departure would leave Johnson’s inability to lead exposed. “All these imitation ERG [European Research Group] groups that are springing up, the Northern Research Group, the Covid Research Group, are a symptom of non-existent party management. “The contempt for MPs does not come from Dominic Cummings, he’s just a harder version of the smiling frontman. The basic contempt comes from Boris Johnson. This is not a guy who does the Commons tearooms, who fraternises with fellow MPs. This is a guy who gets blown around by whatever storm; he has no political compass. “Cummings was his ultimate human shield, the lightning conductor for all the hostility from Whitehall and politicians, but it is Johnson’s leadership that is the problem. He doesn’t like making decisions, he doesn’t like upsetting people, he barely had any experience around the cabinet table before becoming leader,” they said. “He is an outsider, a personality. There’s very little seen of him building a support base within the party.” However, Dominic Grieve, former attorney general and a longtime critic of the outgoing adviser, said Cummings had “created mayhem in government”, with his period at No 10 “marked by a slide in standards”. Grieve said: “This year it’s difficult not to say that he’s created nothing except chaos with the prime minister.” Theresa May’s former chief of staff Gavin Barwell told Radio 4’s Today programme the departure of Cummings and Cain was an opportunity for “more harmonious and more effective” communications, and “to rebuild relations with Conservative MPs, the parliamentary party. And, perhaps, to set a less confrontational and more unifying tone, that is maybe more in tune with [Johnson’s] natural instincts.” Cummings did not answer any questions as he left his north London home on Saturday afternoon, only speaking to reporters to ask them to move out of his way before getting into a Toyota Prius which then drove away.