• Writing in the Telegraph, former cabinet minister Sir Simon Clarke said the Conservatives had lost "key voters" by failing to be bold on immigration.
• And 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."
Image: UK PARLIAMENT
A senior Tory MP has called for his party to replace Rishi Sunak as prime minister or be "massacred" in the general election.
Writing in the Telegraph, former cabinet minister Sir Simon Clarke said the Conservatives had lost "key voters" by failing to be bold on immigration.
But his article was criticised by several other ex-ministers.
Former Home Secretary Dame Priti Patel accused Sir Simon of "engaging in facile and divisive self indulgence".
And 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."
Lee Anderson, who joined Sir Simon in rebelling over the Rwanda Bill last week, said there was "no chance" of Mr Sunak being removed before the next election.
He urged his colleagues to get behind the PM, telling the Telegraph "our only chance to win the next election is by keeping Rishi in No 10".
Home Secretary James Cleverly said he "could not disagree with [Sir Simon] more on this particular issue".
He argued Mr Sunak was succeeding in his attempts to cut inflation and reduce the number of people crossing the Channel in small boats.
"If we were to do something as foolish as have an internal argument at this stage, all it would do is open the door for Keir Starmer," he said.
Sir Simon denied he was "positioning myself or on behalf of another".
"I am speaking out because the stakes for our country and my party are too high to stay silent," the MP for Middlesbrough South and East Cleveland added.
A general election is expected in the second half of this year, with 28 January 2025 the latest date one could legally be held.
Sir Simon is now the second former minister publicly calling for Mr Sunak to resign. Former education minister Dame Andrea Jenkyns submitted a letter of no confidence in the prime minister in November.
After serving as chief secretary to the Treasury while Mr Sunak was chancellor, Sir Simon became an enthusiastic supporter of Liz Truss's leadership bid and joined her cabinet.
A source close to Ms Truss said she "had no idea what Simon Clarke is/was up to and is in no way supportive of what he is saying".
Conservative MPs can only trigger a leadership election if 53 MPs write to the chair of the 1922 Committee requesting one.
In his Telegraph op-ed, Sir Simon said "the Conservative Party under Rishi Sunak once again stands on the opposite, crumbling bank of this widening precipice".
The former levelling up secretary said Tory MPs might be "afraid" of electing a fourth leader in two years but asked: "Which is worse: a week of chaotic headlines in Westminster, or a decade of decline under Keir?"
"Every Conservative MP will need to live with the decision they make in the coming days for the rest of their lives. Failing to act would itself represent a decision," he added.
Sir Simon's comments come after a week of open rebellion against Mr Sunak over his flagship Rwanda Bill, which aims to deter migrants from crossing the Channel in small boats.
Last week 61 Conservative MPs voted to change the bill as it went through Parliament - the biggest rebellion of Mr Sunak's premiership.
In the end their attempts failed and only 11, including Sir Simon, voted against the bill as a whole.
But debate over the legislation exposed ongoing divisions within the party, with two deputy chairmen, Mr Anderson and Brendan Clarke-Smith, quitting their roles in order to vote for changes.
It is not anticipated that two of the most prominent rebels - former Home Secretary Suella Braverman and former Immigration Minister Robert Jenrick - are about to join calls for the PM to go.
However, Mr Sunak's critics say discontent with his leadership extends beyond the Rwanda rebels.
'Utterly ludicrous'
Jonathan Ashworth, a Labour shadow cabinet minister, said Sir Simon's article revealed just how divided the Conservative party is.
Mr Ashworth said: "It doesn't matter who leader is because the party is divided from top to bottom."
Liberal Democrat Deputy Leader Daisy Cooper said it is "utterly ludicrous that the Conservative Party is even discussing installing a fourth prime minister without giving voters a say".
Mr Sunak is the third Conservative prime minister since the 2019 election, after MPs deposed both Boris Johnson and Liz Truss in 2022.
There has been a sense of gloom among Conservatives over the past few weeks as Mr Sunak's repeated attempts to gain the upper hand politically have failed to make a dent in their standing, with the party trailing Labour by 18 points in polls.
A general election poll of 14,000 people by YouGov projected Labour was on course for a 120-seat majority as things stand.
If accurate, the poll would mean "more Tory seats being lost than in 1997, the Red Wall being wiped out completely and shocking defeats in historic Tory constituencies like Chichester, Horsham and Banbury," Sir Simon said.