Boris Johnson is facing a fresh threat from Conservative rebels planning a takeover of the powerful backbench committee that could force the prime minister from office. Opponents of Johnson, including some who were loyal to him as recently as last week, have set their sights on a “clean sweep” of the 1922 Committee amid a hardening of the mood against the prime minister. The committee has the power to change the rules to allow a new vote of no confidence in Johnson within 12 months, and as soon as this autumn. In a secret ballot to decide its executive members, which will be held within three weeks, rebels hope to seize all 18 positions that are up for grabs. The contest will be viewed as a proxy vote on whether the prime minister should face another no-confidence ballot, after this month’s saw more than 40% of his MPs oppose him. Opposition to Johnson has hardened in the past week after a disastrous double byelection loss, his open pursuit of a third term and a series of scandals. Two previous supporters of the prime minister told the Guardian they would not back him in another confidence vote, while negotiations have begun to agree a unified slate that would ratchet up pressure on the prime minister to quit. Several “pork pie plotters” – a group of Tory MPs elected in 2019 who met to discuss Johnson’s demise in February – have recommenced talks. Other caucuses, such as the One Nation Conservatives and Thatcherite “92 Group” have also been quietly approached to ensure the slate reflects a broad range of MPs. The campaign to oust Johnson in the last no-confidence vote was disjointed, but rebels are said to be “getting ruthlessly organised”. Among those considering a run for 1922 Committee seats are five Tory MPs who have been critical of Johnson’s handling of the Partygate scandal. Steve Baker and Andrew Bridgen have declared their intention to run; others contemplating the same include Aaron Bell, who submitted a letter of no confidence in Johnson in February, and Paul Holmes, who quit as a ministerial aide over Partygate. Chris Green, a former minister who said Johnson faced the “greatest political challenge to survive” after the recent no-confidence vote, is also planning to stand. One MP said: “We’ve got to make sure this is done properly – there’s no room for mistakes like last time. We need to make sure there isn’t a split in the vote because there will almost certainly be a pro-Boris slate, too.” Only backbenchers are allowed to vote in the 1922 Committee election, whose likely date could be announced next Wednesday. MPs crunching the numbers from the last no-confidence vote believe that given 41% called for Johnson to quit and that most in government can be relied on to have remained loyal, the vast majority of those who will get a say in the 1922 Committee election are opposed to his leadership. Some current members of the committee are understood to want to cut the time Johnson is immune from another challenge to his premiership from 12 months. While the controversial move would not happen immediately, it would be a possible emergency course of action should Johnson be damaged further by the privileges committee investigation into whether he misled parliament over Partygate. The 1922 Committee has an 18-strong leadership group. Of the 10 current executive members, four are seen as being publicly supportive of the prime minister. Two have stepped down after becoming parliamentary private secretaries. Five of the committee’s six officers are believed to oppose Johnson. While some rebels said they were aiming for a “clean sweep” of the positions, one insisted it was not about “kicking off all pro-Boris” members but ensuring there was a sufficient number who “would be open to listening to how people genuinely feel”. Government whips are understood to be keen to avoid appearing to interfere in the selection process. But supporters of the prime minister fear the contest will have echoes of the no-confidence vote, when his allies in government were seen as being too hands-off. “There’s a misplaced confidence going on again,” one admitted. While a decision about whether to change the rules will be up to the new committee, the former Tory party leader Iain Duncan Smith said it would be “shifty” for the decision to be taken by a handful of MPs. He called instead for the full parliamentary party to be balloted about such a move. Some rebels are uncomfortable about “changing the rules in the middle of the game” and instead want to “use other mechanisms” including putting pressure on Conservative association chairs and party donors to publicly call for the prime minister to be replaced. “Every day Boris goes on is another day wasted when we could be having a leadership contest and be drawing a line under this,” said one. A slate of anti-Johnson candidates could also rile some wavering Conservative MPs, who believe the 1922 Committee should assist with boundary and selection issues rather than focusing mainly on leadership issues. Johnson has lost some supporters over the past week due to the recent byelection results, which saw the Tories lose Wakefield in West Yorkshire and Tiverton and Honiton in Devon, prompting the resignation of the party co-chair Oliver Dowden. Their anger was further compounded by the prime minister saying he was “actively thinking” about a third term, his refusal to undergo a “psychological transformation”, and sleaze scandals including allegations he tried to secure taxpayer-funded jobs for his partner and secure £150,000 from a party donor to build a treehouse at Chequers. Earlier this week, Johnson refused to comment on the unhappiness of some MPs, saying he would not engage in political commentary. Some backbenchers who voted against him earlier this month have said they will respect the result and urged colleagues to do the same. Andrea Leadsom, the former business secretary, told the BBC on Wednesday: “There was a confidence vote, he won it … Whether the media like it or not, we then move on.”