David Cameron's leadership was under fresh scrutiny last night after it was claimed Boris Johnson had discussed a dramatic return to the Commons with a Tory MP, and another member of the party revealed a short-lived scheme to topple the Prime Minister.
In a meeting with Mr Johnson, Zac Goldsmith is said to have raised the idea of quitting as MP for Richmond Park in protest over any plans to expand Heathrow Airport and stepping aside to allow Mr Cameron's greatest rival to stand in the resulting by-election.
Meanwhile, the Tory MP Bob Stewart disclosed that two colleagues asked him to mount a "stalking horse" challenge to Mr Cameron designed to force him out of Downing Street. He told them to "get lost" and said he would never contemplate such disloyalty to his leader.
Neither plot got off the ground, but their existence underlines the disillusionment among a minority of Conservative backbenchers over Mr Cameron's leadership. It is likely to intensify if Tory support falls in the opinion polls and economic recovery remains elusive.
Mr Johnson and Mr Goldsmith, one of the Prime Minister's most vociferous critics, met last week to discuss how to co-ordinate resistance to the expansion of Heathrow. The issue was put back on the political agenda when Justine Greening, a vehement opponent of a third runway at the airport, was removed as Transport Secretary in last week's Government reshuffle.
According to the Mail on Sunday, Mr Goldsmith told Mr Johnson that he was ready to quit as an MP if the scheme went ahead, which would allow him to contest the by-election.
The London Mayor – who is widely regarded as the front-runner to succeed Mr Cameron, but first needs to return as an MP – is said to have dismissed the suggestion "out of hand".
The two men confirmed they met last week to discuss Heathrow, but played down reports of the by-election plot.
Mr Goldsmith said: "We covered all sorts of possibilities." The Mayor's spokesman said: "It's no surprise the Mayor has met and will continue to meet those who share his concerns over the lack of aviation capacity in London and the south-east. But the story in question is without doubt fanciful."
The by-election plan would depend on Mr Cameron declaring his support for a third runway before the general election due in May 2015, which looks highly unlikely – although moves to increase the number of night flights into Heathrow could be announced next year.
Colonel Stewart, the MP for Beckenham, who was the commanding officer of British forces in Bosnia, said that he was approached by two Tories before the parliamentary summer recess and asked to stand against the Prime Minister as Conservative leader. The aim would have been for him to collect enough support to wield a fatal blow against Mr Cameron, enabling heavyweight candidates to enter the contest at that point.
He said: "It was a silly suggestion that I dismissed. I told them to get lost. I was not having anything to do with it."
Colonel Stewart declined to name the plotters and said he had not been told on whose behalf the pair were operating.