The Conservative party finds itself in disarray over the renewed possibility of a third runway at Heathrow, after thinly veiled jibes at the prime minister from a senior Conservative MP.
Tim Yeo has demanded that David Cameron reveal whether he is "man or mouse" over the issue in an article for the Telegraph newspaper.
Yeo, chair of the Commons' energy and climate change committee and formerly chair of its environmental audit committee, had previously opposed another runway at Britain's main international hub airport.
But he has changed his mind and is now at the vanguard of Conservative backbenchers calling on the government to change its mind.
"An immediate go-ahead for a third runway will symbolise the start of a new era, the moment the Cameron government found its sense of mission," he urged.
"Let's go for it."
Conflict over Britain's future aviation strategy has been developing for some time behind closed doors.
Chancellor George Osborne is thought to have been calling for the issue to be reopened, but Cameron is understandably reluctant to do so: the Tory party's 2010 general election manifesto made clear it would not support a third runway and the coalition agreement ruled out such a move.
Transport secretary Justine Greening, whose Putney constituency is over the Heathrow flight path, made clear on the Today programme this morning she would find it "difficult" to remain in the Cabinet if a third runway was revisited.
Her position has come under intense scrutiny because of next month's looming reshuffle. Greening has only been at the Department for Transport for ten months, so moving her away from the job would send a clear signal that Cameron is preparing the ground for a policy U-turn.
Doing so would please large swathes of the Conservative backbenches. This year has seen the Free Enterprise group of Tory MPs break ranks, backed by business groups arguing that Britain is falling behind countries like France and Germany.
It is the tone of Yeo's criticisms which will prove most immediately concerning to Cameron, however.
"The prime minister must ask himself whether he is man or mouse," Yeo wrote.
"His place in history is assured as the leader who made the Tories (nearly) electable again, an achievement that eluded three previous leaders.
"But 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?"
References to the electoral elusiveness of Cameron's heart – and his failure to win an outright majority in 2010 – will not go unnoticed by Tory party observers, least of all in No 10.
Yeo would not retreat from his provocative position in an interview on The World At One programme this lunchtime.
"This is a moment of opportunity for the prime minister," he declared.
"The circumstances in which the original Conservative commitment in 2008 not to have a runway were quite different… It's a mark of mature and effective leadership for a government to be able to say… the [economic] situation has developed in an unhelpful way."
He was attacked by fellow Tory MP Bernard Jenkin, who told the same programme: "I very much regret this ad hominem tone Tim has adopted. I think it's very discourteous to David Cameron - he's not going to be bamboozled by being bullied.
Changing the government's opposition to a third runway at Heathrow would leave Cameron exposed to 'broken promises' accusations. As Jenkin added: "His credibility would be completely shot if he departed from that on a personal basis."
Election literature for the 2010 campaign had warned there were "just days left to stop Labour's third runway". Cameron was quoted as saying: "No ifs, no buts, no third runway."
Greening pointed out that the purported third runway would not be long enough for the largest aircraft as she argued the situation had not changed since 2010.
"The coalition agreement is very clear that we don't support a third runway and there's now cross-party consensus… but what we do need to do is start the process of saying if we're not going to have a third runway, how do we make sure we've got the hub capacity our country needs going forward? That's the process I'm about to start when parliament comes back," she said.
"It is time to move away from what we've had in the past – a piecemeal approach to aviation strategy. What we need to do is look long-term, start to be more bold.
"The process I'm about to kick off is one that will see us come up with a better, longer-term solution."