Simon Clarke, a former Cabinet minister, is facing backlash from Tory MPs after launching an attack on Prime Minister Rishi Sunak.
Writing in The Daily Telegraph on Tuesday, Clarke claimed Sunak was "leading the Conservatives into an election where we will be massacred".
He added: "He does not get what Britain needs. And he is not listening to what the British people want."
But several senior Conservative MPs swiftly criticised his remarks, including the former home secretary Priti Patel, who said: "Engaging in facile and divisive self-indulgence only serves our opponents".
Tobias Ellwood accused Clarke of "throwing his teddies in the corner" because "his choice of prime minister is no longer in No 10".
Sir David Davis, a former Brexit secretary, said: "The party and the country are sick and tired of MPs putting their own leadership ambitions ahead of the UK's best interests."
The postal affairs minister, Kevin Hollinrake, said Clarke's intervention on Tuesday night was a sign of the "panic" that is brewing in some factions, but said it was not a view held by the wider parliamentary party.
He labelled the intervention "dangerous, reckless, selfish" and "defeatist" and urged Clarke and his allies to realise that voters want "unity, unity, unity".
The Prime Minister is under increasing pressure after he was dealt a blow to his Rwanda deportation plan – The House of Lords voted to delay ratification of the treaty with Kigali.
A majority of peers – 214 against 171 – voted to delay the approval of the treaty until the British government had demonstrated that Rwanda was a safe country for migrants who would be deported there.
The vote ramped up pressure on Sunak, just days after he narrowly survived a significant backbench rebellion over the Rwanda bill in the House of Commons.
Two deputy chairmen of the Conservatives resigned from their roles as they joined dozens of Tory right-wingers, including ex-PM Boris Johnson, in backing amendments to toughen the scheme.
Sunak has staked his political future on tackling illegal migration, promising to "stop the boats" of migrants crossing the Channel from northern France.
A confidence vote in the prime minister will be triggered if 53 Tory MPs submit letters to the 1922 Committee. So far, Clarke and the former minister Dame Andrea Jenkyns are the only Conservative MPs who have publicly called Sunak to go.
After serving as chief secretary to the Treasury while Mr Sunak was chancellor, Sir Simon enthusiastically supported Liz Truss's leadership bid and joined her cabinet.
But a source close to Ms Truss said she "had no idea what Simon Clarke was up to and is in no way supportive of what he is saying".
The former defence minister Ben Wallace has also weighed into the row, criticising Clarke's remarks in an article for The Telegraph, insisting "division and another PM would lead to the certain loss of power".
"My colleague Sir Simon Clarke is wrong," Wallace wrote, "The way to win the next election is to tackle inflation and grow the economy.
"Rishi is doing just that. Division and another PM would lead to a certain loss of power. We need to focus on delivering for the public, not divisive rowing."
A new poll released earlier this month showed The Conservative Party are potentially on course for their worst electoral defeat since 1997.
A YouGov survey of 14,000 respondents forecasts that The Tories will hold on to just 169 seats, while Labour will claim 385.
This would deliver Sir Keir Starmer's party a majority of 120 seats in the upcoming General Election, which has to be held before the end of the year.
Sunak insists his party are making progress on his five key pledges, including bringing inflation down and curbing illegal migration.
