It is, perhaps, a reflection of the calamitous state of Britain's economy that the Heathrow third runway question is once again on the table.
"No ifs, no buts, no third runway," the campaign leaflet declared. The Conservatives couldn't have been clearer in their 2010 election literature that, if they got into power, New Labour's plans to expand Heathrow wouldn't go ahead. The necessities of coalition forced some compromises with the Liberal Democrats, but aviation strategy wasn't one of them. Under the Tories and the Lib Dems, Labour's third runway looked dead and buried.
Now, as the coalition's third year drags miserably on, the game has changed. Britain languishes in a double-dip recession. Impulses towards getting the economy moving again have, for many Tory MPs worried about their seats and Tory ministers worried about their government, grown steadily stronger. For many they are now irresistible.
Business lobby groups have been steadily increasing their calls for a rethink, warning that without action Britain will fall behind Germany and France as a major international aviation hub. Both already have more routes to China than Britain, for example. After many months of slowly building pressure, the prime minister finds himself being asked publicly whether he is a "man or a mouse" over the issue.
'All of our customers are international and we need those transport links to be as efficient and effective as possible'
Elizabeth Truss doesn't approve of the tone Tim Yeo used for that very overtly personal attack on David Cameron's leadership. Still, she stands by her call for expansion at Heathrow. "For me, this is an issue about how we make the British economy competitive," she says. Truss is the convenor of the Free Enterprise Group, a loose band of very enterprising new-ish Tory backbenchers whose recent Policy Bites paper backed not just a third but a fourth runway at Heathrow, too.
"We do need a hub airport in the south-east of England," Truss says. "If you want to have a hub airport three runways probably isn't enough. If we're imaginative about Heathrow, I don't see why we can't build four runways there." Heathrow is the hub airport at the moment, so the additional costs of moving it elsewhere would be avoided by expansion. And closing Heathrow as a hub would have a "massive" impact on local businesses. Whereas expanding Heathrow would make"connectivity" with rail and road easier, too.
Reversing the government's position, though, is easier suggested than done. This has already been a bumper year for coalition U-turns. One of this size and significance would not go down well among the many Tory MPs who saw their majorities boosted by opposition to Labour's third runway in 2010. Among them is transport secretary Justine Greening; another is Zac Goldsmith, the Conservative MP for Richmond Park and North Kingston, who went so far as to promise to voters he would immediately resign if his party changed its policy on the issue.
"This is a really big decision," Goldsmith says. "Going down the Heathrow route means effectively plunging a lot of people into what they would describe as a nightmarish situation. Any representative of this area is obliged to do whatever they can to prevent this from happening."
Goldsmith, who is deeply worried by the breakdown in trust between politicians and voters, believes that the value of an election manifesto will be badly damaged if the Tories do change their mind. A U-turn, he believes, would "make it hard, even for people like Elizabeth Truss, to persuade anyone whose door she knocks on in 2015 that the manifesto she's standing on means anything".
Truss is more relaxed about this issue. "There is not going to be a third runway going to be built in this parliament," she shrugs, "so as far as I'm concerned we're honouring the pledge in that manifesto."
Maria Eagle, the shadow transport secretary, doesn't mind changing her party's position, either. "We lost the general election," she says simply when I ask her why Labour decided to oppose a third runway. The coalition government cancelled Labour's proposals, she says, and that "changed the situation" pretty drastically. It was no coincidence that new leader Ed Miliband, his time at the Department of Energy and Climate Change still fresh in the memory, had always been uncomfortable with the proposals.
The U-turn has divided the party: former chancellor Alistair Darling is among those who have called for another change of heart. Senior members of the current shadow Cabinet reportedly think Miliband would be sensible to shift position. Like the Conservatives, Labour are finding agreement on aviation strategy elusive.
Eagle says she's "not surprised" that some in her party think expanding Heathrow is the right way forward. Beyond ruling out the 'Boris island' Thames Estuary airport (it's a "non-starter", she says simply) - she is not offering any hard-and-fast solutions to the problem. Yes, further growth is needed. If not another runway at Heathrow, then where? Gatwick and Stansted both have more capacity available, but there are concerns about the rail and road links connecting them to the capital. Goldsmith believes these should simply be expanded, allowing these airports to grow while keeping Heathrow as it is.
Rather than offering any answers of her own, Eagle wants more consideration of the options available. She fears a repeat of the post-2010 scenario in which a general election results in a change of policy, resulting in no progress whatsoever. Unfortunately, proposals for cross-party talks to try and achieve a consensus that will last beyond 2015 haven't met with a positive response from the coalition. Because of their own troubled internal divisions, presumably.
"At the very least we've got to try and get a consensus that means we don't have that difficulty," Eagle urges. "They've got to step up to the plate if they're going to run the country in a way that's good for the economy and for the people who are going to be affected by this. Instead of press-release politics... they've got to say, what is the appropriate future for aviation while meeting our climate change targets and mitigating local environment impact?"
Ah, yes - the environment. Once it was impossible to think about aviation strategy without jumping immediately to the drive to lower carbon emissions. Nowadays the economy is uppermost in the minds of some, although it remains important to others.
The Liberal Democrats, for example. Concerns for the environment have been a big part for the coalition's junior party instinctive opposition to a third runway for some time, and that remains the case today. Still, Julian Huppert, the MP for Cambridge and the party's backbench spokesperson for transport issues, acknowledges there is capacity within the carbon budgets for an increase in aviation usage up to 60% beyond current levels.
"That is allowing for a range of technological improvements," he notes. "It does mean there would be a higher proportion of emissions coming from aviation. What there isn't scope for is unlimited capacity growth."
With Stansted at roughly 50% capacity, Huppert states simply that a third runway at Heathrow "simply doesn't make sense". A quarter of all people affected by aircraft noise in Europe are located in west London under the Heathrow flight path. Yet he concedes that in the long-run it may end up being the best option. Huppert wants the Lib Dems to approve a policy motion backing a detailed, in-depth independent look at the options for the medium- and long-term.
Truss would also like to see more analysis. "There were studies under the previous government, but they're quite old now. I'd like to see definitive evidence on the different sites," she says. Free Enterprise Conservatives believe the short-term vs long-term clash could be dealt with by simply constructing four runways, not three, at Heathrow. This would end the 'stopgap' objection once and for all.
It would also trigger a by-election in Richmond. "I think politicians will always prefer to have a single solution, as opposed to having to trouble themselves of the details of something that is much more complex," Goldsmith says. A single runway would lead to an extra 23 million road passenger journeys a year to Heathrow, he claims. "My very strong feeling is most of the people who are really pushing for a third runway are people who haven't really looked at the facts. It doesn't add up."
At the moment, all three parties' official policy is that Heathrow will not be expanded. All acknowledge that Britain is falling behind and needs some kind of aviation expansion, though. As well as the four London options of Boris Island, Gatwick, Stansted and Heathrow, a number of regional airports are enthusiastic about growing - and have local MPs earnestly supporting them. Finding agreement on a national way out of all these confusing, often strongly held views is not going to be easy.
Over the coming months the government will finally begin its formalised search for answers. A national discussion will take place in which the Conservatives, Labour and the Liberal Democrats seek long-term answers to a problem which demands a decisive answer sooner rather than later. Given the difficult positions both Cameron and Miliband find themselves in, room for movement seems limited. All the signs are this debate is going to run and run.