Patrick Mercer, a former Army officer, has become the first Conservative MP to be named as one of a group of 14 who have written letters saying they want a challenge to David Cameron's leadership.
The MP for Newark, a former colonel who was the first member of the Tory front bench to be sacked by Mr Cameron five years ago for remarks he made about racism in the Army, was named yesterday in the Mail on Sunday.
It would take 46 Tory MPs to write individually to the chairman of the 1922 Committee, which represents backbench opinion, for Mr Cameron to face a leadership challenge.
Such an uprising is highly unlikely this year, especially since the UK's most popular Tory politician, London's Mayor, Boris Johnson, is not eligible to run as he is not an MP. But the Prime Minister's position may become unsafe if the Government continues to trail in the polls and Mr Johnson finds a safe seat.
Yesterday, Mr Cameron received support from the last person to head a Conservative government. Sir John Major, who entered Downing Street after Margaret Thatcher was forced out of office by a leadership challenge in 1990, told the BBC's Andrew Marr Show: "If the Conservative Party has learned anything in the last 20 years, it's learned that regicide is not a good idea."