Boris Johnson is “on notice” and could be gone within a year unless he cleans up his act and shakes up his No 10 operation, senior Tories are warning, after the Liberal Democrats scored an extraordinary victory in the North Shropshire byelection. The Conservative party chair, Oliver Dowden, conceded on Friday that voters had wanted to give the government a “kicking” because they were “fed up” with “sleaze allegations”. But Johnson himself did not appear repentant about the accusations of parties in No 10 during lockdown, or the scandal over his attempt to water down the MPs’ standards system that led to the North Shropshire byelection. In an interview, the prime minister said he took responsibility for the loss but also blamed the media and public for focusing too much on “politics and politicians” rather than real issues. Veteran backbencher Roger Gale said Johnson was now in “last orders time” and warned that “one more strike and he’s out”. Ruth Davidson, the former Scottish Tory leader, told the BBC that the prime minister was “drinking in the last chance saloon” and that MPs were “looking for a bit of bloody grip to be exerted”. Other senior Tory MPs vented their fury at what they regard as a self-inflicted defeat, and urged the prime minister to implement a radical overhaul of his Downing Street team. There was particular anger among Tory MPs on Friday about the allegations that Simon Case, the cabinet secretary charged with an inquiry into No 10 parties during lockdown, had been aware of a Christmas party held by his own private office. Iain Duncan Smith, the former Tory leader and cabinet minister, urged the rebels to stop talking about a new leader but also warned that Johnson would need to make changes over the alleged breaches of lockdown rules among No 10 staff. “The prime minister just needs to show us really strongly that he not just disapproved, but he’s prepared to get rid of people who are breaking those rules, so he can move on,” he told the BBC. “He needs to be out front as the great political salesman, not bogged down having to, you know, apologise, and to find out what’s going on. That is never good for any leader no matter … how good they are. But he needs to be upfront.” The Tory MPs are demanding changes to Johnson’s staff despite allegations the prime minister was himself aware of lockdown-breaking gatherings and present at some of them. A former Tory cabinet minister warned Johnson’s operation needed a change. He said that Johnson still has a chance of resetting his premiership, but added: “There are those who say, Boris can’t change. And the consequence of that is a better-than-50% chance he’ll be dead by the end of next year.” Underlining the need for Johnson to overhaul his approach, they said: “The old Boris brand, the old Boris shtick, doesn’t work any more.” Another Conservative former cabinet minister said MPs were already discussing among themselves how to get the prime minister to change his top team, and in particular, expressing reservations about his chief of staff, Dan Rosenfield. He said MPs would be delivering a message to Johnson that he needed to shake up his operation and consult more with MPs, with the scale of discontent obvious after 100 rebelled against his plan B Covid measures this week. “He needs to reassess a few things, in particular No 10 itself … there is a very inexperienced complement of staff there who would not be behaving in the way they clearly have been behaving if they had been more mature. The chief of staff clearly hadn’t sufficiently strong oversight of them. It is undergraduate behaviour that you don’t expect from people operating at the centre of the government.” But one minister said that Johnson was unlikely to be able to change his approach. “He’s probably not going to come to terms with the fundamental questions he’s got to ask himself – he never has and I doubt he will. At some point people won’t forgive him any more … He’s on notice, from me.” Helen Morgan, the new Lib Dem MP for North Shropshire, clinched the formerly safe Conservative seat with an extraordinary 34% swing. She won 17,957 votes, 5,925 more than the Conservatives’ Neil Shastri-Hurst, while Labour’s Ben Wood was third with 3,686. Turnout was 46.3%. The byelection is the second the Lib Dems have snatched from the government in six months, after their victory in Chesham and Amersham. Hailing the result, the Lib Dem leader, Ed Davey, said: “From Buckinghamshire to Shropshire, lifelong Conservatives have turned to the Liberal Democrats in their droves and sent a clear message to the prime minister that the party is over.” Interviewed afterwards, Johnson appeared reluctant to accept that his own behaviour was the cause of the historic swing against the Tories. “Basically what’s been going wrong is that in the last few weeks some things have been going very well, but what the people have been hearing is just a constant litany of stuff about politics and politicians: stuff that isn’t about them, and isn’t about the things that we can do to make life better,” he told Sky News. The byelection was sparked by the resignation of the veteran Brexiter Owen Paterson after a botched attempt by the prime minister to prevent him being punished for paid lobbying. Johnson’s decision to back Paterson crystallised Tory MPs’ concerns about his political judgment, and his authority has continued to be battered by a string of missteps and scandals. Labour have pulled ahead in the polls over recent weeks, since news of a string of parties in Downing Street began to emerge. At the same time, Johnson’s backbenchers have also become increasingly rebellious and fractious, with 100 of his own MPs voting against Covid restrictions on Tuesday. The sizeable revolt against Covid passports and face masks in more public places has now made it difficult for Johnson to ask parliament to bring in more measures against Omicron, despite a record number of cases recorded on Friday at 93,045. Johnson’s team will be hoping for a relaunch of his leadership after Christmas, with a focus on levelling up as Michael Gove brings forward his white paper. No 10 is also focused on the government’s booster campaign, with Johnson warning on Friday that a “big wave” of Omicron is now “coming through”. One longstanding Johnson supporter, Tory MP James Duddridge, insisted the byelection was just an example of “lumps and bumps” of midterm government, and claimed the prime minister would weather the storm. “He gave us an 80-seat majority … we get beyond Covid and everyone gets a bit more reassured. Yes, the electorate gave us a kicking. Yes, it was bloody stupid on the standards report. But mistakes will be made.”