A senior Tory MP has challenged David Cameron to decide whether he is a "man or a mouse", in the latest in a series of backbench attacks on the government.
In a strongly worded personal criticism on the prime minister, the chairman of the Commons energy committee Tim Yeo said Cameron should ditch his pre-election pledge to block a third runway in order to boost economic growth.
Writing in the Daily Telegraph on Tuesday, Tim Yeo said: "The prime minister must ask himself whether he is man or mouse.
"Does he want to be another Harold Macmillan, presiding over a dignified slide towards insignificance?
He added: "Or is there somewhere inside his heart – an organ that still remains impenetrable to most Britons – a trace of Thatcher, determined to reverse the direction of our ship?"
Yeo's sharp criticism of the prime minister is the latest in a series of bold backbench attacks on government policy.
Tory MPs succeeded forcing the coalition to ditch its plans to reform the House of Lords earlier this month, much to the anger of the Lib Dems.
While chancellor George Osborne was also pressured into performing a series of U-turns over his infamous 'omnishambles' Budget including the so-called Pasty Tax and Caravan Tax.
Many Tory MPs have also been highly critical of Cameron's approach to the European Union, unhappy with his refusal to hold a referendum on Britain's membership.
Any decision by Cameron to reverse his pre-election position on Heathrow and sanction the expansion of the West London airport would be seen as possibly his biggest U-turn to date.
In the run up to the 2010 general election the Conservatives decided to oppose expansion plans, with Cameron unequivocally declaring: "No ifs, no buts, no third runway".
And Nick Clegg said today that the government would not "lurch" to changing its position just because "one MP" had said it should.
He told a manufacturing firm in North Tyneside: "We're not going to give the go-ahead to the third runway at Heathrow because we said very clearly as both parties that we wouldn't do so, so we're going to stick to the Coalition agreement.
"My position is very clear - we're not going to give the go-ahead to a third runway at Heathrow. We said that in the Coalition Agreement and we're going to stick to that."
A change of heart would also put transport secretary Justine Greening in an impossible position as she led the campaign against the airport's expansion while in opposition.
Greening, whose Putney constituency lies underneath the Heathrow flight path and was only given the transport job in October, indicated she could be forced to quit if she was overruled.
Asked by the BBC Radio 4's Today programme on Tuesday morning if she could stay in the cabinet she said: "I think it would be difficult for me to do that."
"The coalition agreement is very clear we don't support a third runway, there is cross-party consensus," she said.
On Tuesday morning Olly Grender, one of Nick Clegg's top aides, alluded to the row when she Tweeted that Larry the Downing Street cat was sat "proudly outside No10 front door with a dead mouse next to him".
Yeo is not the only senior Tory to come out in favour of airport expansion. Housing minister Grant Shapps warned a third runway was needed to ensure the UK remained a "great trading nation" and Mayor of London Boris Johnson accused Cameron of "pussyfooting around".
Tory pressure to expand Heathrow follows disappointing economic growth figures, with Yeo insisting a third runway was "desperately needed" to make Britain "the most business-friendly country in Europe".
Speaking to ITV news on Tuesday, Yeo suggested that Greening should be prepared to be moved out of her job.
"I think that Putney has issues which she quite rightly has to champion," he said. "Maybe another portfolio in the cabinet might suit her better."
A poll conducted for The Guardian on Tuesday showed that George Osborne has peaked in unpopularity , with just under half of voters wanting the chancellor replaced in David Cameron's widely-expected Cabinet reshuffle.