Downing Street has insisted that the Government will not back down on its opposition to a third runway for Heathrow, amid growing unrest among Tory MPs over Britain's future airport capacity.
No 10 brushed off an outspoken attack by senior Conservative backbencher Tim Yeo who challenged David Cameron to show if he was "man or mouse" and defy his critics by reversing policy on the issue.
His intervention prompted fresh demands from fellow Tories for ministers finally to grasp the issue and address the country's long-term aviation needs.
Ministers could be in for a rough ride when MPs return to Westminster next week following the summer break, with concern over the issue tapping into a wider sense of unease about the struggling economy.
Downing Street insisted the Government is sticking by its commitment in the coalition agreement that there would not be a third runway at Heathrow.
"The coalition parties have made a pledge not to have a third runway and that is a pledge that we will keep. We don't see the argument for a third runway," a No 10 spokeswoman said.
Transport Secretary Justine Greening, whose Putney constituency lies under the Heathrow flight path and who has campaigned against a third runway, warned she would find it "difficult" to remain in the Cabinet if the policy changes.
Nevertheless she will be under pressure to press ahead with the promised consultation on future airport capacity, with Chancellor George Osborne reported to be among those warning that the future needs of business must be addressed.
Mr Yeo, a former environment minister and chairman of the Commons Energy and Climate Change Committee, denied that he is "throwing down a gauntlet" to the Prime Minister.
Writing in The Daily Telegraph, he said that an immediate decision to give the go-ahead to a third runway would show that his Government has found its "sense of mission".
He 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? 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?"
While some Tories were dismayed at Mr Yeo's "discourteous" attack on their leader, it nevertheless prompted fresh calls for Mr Cameron to get on and tackle the issue.
Boris Johnson favours a new airport built in the Thames Estuary, dubbed "Boris island". He said that while the Prime Minister is right not to be "stampeded" into a change of policy, the problem would not go away.
The London Mayor, seen as a potential leadership challenger to Mr Cameron and who has previously criticised the Prime Minister for "pussyfooting around", drew back from a fresh personal attack but urged him to "seize the moment".
Mr Johnson said: "I think he's a man of dynamism and greatness and he will seize the moment to give this country the long-term solution that it needs.
"It is plain the argument over aviation capacity is not going to vanish. You can't long-grass this. It is necessary to come up with an answer. Business needs an answer and I've no doubt the Prime Minister is going to provide one. They have moved a long way. They have shown great foresight in abandoning a position that said no runways ever, and they are now looking at expanding aviation capacity.
"The question is where and I think the Prime Minister is absolutely right not to be stampeded by one side of the argument or the other."
He was supported by Bernard Jenkin, Conservative chairman of the Commons Public Administration Committee, who said that an airport in the Thames Estuary is a "no-brainer".
Mr Jenkin said: "If you take anything more than a 10 or 15-year view, then a new airport on an entirely new site becomes the only option."
Deputy Prime Minister Nick Clegg, who remains firmly opposed to a third runway, acknowledged that ministers would have to consider other options to meet the country's aviation needs.
"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," the Lib Dem leader said.
"But that doesn't mean we're going to stick our heads in the sand over the aviation debate about capacity in this country. There are lots of ways of doing that and we shouldn't just lurch to one solution because one individual MP was to say so."
Ms Greening also said that there was a need to be "bold" and consider what the country would need in 50 years, including the possibility of a new hub airport.
"It's clearly one of the options," she said.