"The road to economic recovery isn't a road - it's a flight path." That's the message currently plastered all over the London underground, courtesy of Heathrow owners BAA.

The company's new campaign to reopen the third runway debate is a self-serving effort to play on people's economic anxieties at a time of fear, that much is obvious. But more than that, it's a con - both politically unrealistic and, more importantly, economically incoherent.

After all, even if David Cameron and Nick Clegg performed the mother of all U-turns and reneged on their totemic commitment not to pave over west London, there wouldn't be planes taking off from a new runway for at least a decade. And so it seems that BAA and its supporters have staked out territory for themselves as the most pessimistic of sages when it comes to when this country will bounce back from its economic malaise. They're putting the date of recovery at some point in the 2020s.

Despite their breathless and exaggerated claims about the supposed economic need for expansion at Heathrow, even the former Chief Executive of British Airways, Bob Ayling, has written (£), "A third runway at Heathrow is against Britain's economic interests." Equally, a report from the respected economic consultancy CE Delft looked at the business case BAA made for the runway and found it wanting. So did the Economist magazine, which opposed the plan for the same hardheaded economic reasons.

Even Cameron, before the election, accused Gordon Brown of "faking" the economic case for the runway. He also said, "What business needs to recognise is that the third runway is just not going to happen... There is such a coalition of forces against it. There's such an environmental case against."

Indeed, the arguments over Heathrow expansion remain fundamentally unchanged. As recently as last year, the global property consultants Cushman & Wakefield found that "London is still ranked -- by some distance from its closest competitors -- as the leading city in which to do business" and also concluded it has the best international transport links of any city in the world. And as Chris Goodall points out, BAA are not dealing with the uncomfortable fact that flying for business purposes is down about 25 per cent since the turn of the century. UK residents made 8.9 million business trips abroad by air in 2000 and 6.6m in 2010. Similarly, total passenger numbers in the UK are down over 10 per cent since 2007.

Never mind, it seems, here we go again.

Were "premier league" sums - or visits to his Number Ten Flat - behind the Prime Minister's apparent change of heart? We will likely never know. But according to the front pages of Sunday's Independent and Observer, the cross-party consensus of opposition to Heathrow expansion is breaking down because senior Conservatives led by Cameron and George Osborne are apparently looking to reopen the third runway debate.

Never mind that five major airports already serve London. Or that there are already more flights from Heathrow to China than there are from Paris Charles de Gaulle and Frankfurt combined. The aviation industry lobbyists want more, more, more. As Labour's former aviation minister Chris Mullin wrote:

There is a long history of undertakings being given in return for controversial airport expansions which are either quietly forgotten or cynically abandoned once they becoming inconvenient. During my 18 undistinguished months as a minister whose responsibilities included aviation I learned two things. First, that the demands of the aviation industry are insatiable. Second, that successive governments have usually given way to them. Although nowadays the industry pays lip service to the notion of sustainability, its demands are essentially unchanged. It wants more of everything - airports, runways, terminals.

Any attempt to U-turn on the Heathrow runway will face a fierce political backlash. Within 24 hours of the briefings in the Sunday newspapers, London Mayor Boris Johnson - seeking votes in west London where the runway proposals are politically toxic - said, "It will not be built so long as I am Mayor of London." Richmond MP, Zac Goldsmith, said he'd resign and trigger a by-election if David Cameron reneged on his promise. Similarly, it strikes me it would be impossible for rising star Transport Secretary Justine Greening to remain in post given she is most known for her leading role in fighting the runway plans. Certainly her constituents under the flight path would never forgive such a betrayal. Finally, Nick Clegg knows an about-face on this issue would be as totemic as his tuition fees U-turn. He tied himself to the movement against the runway - even planting a protest tree on the land that would be required to build it - and a change in his position on this would be deeply unpopular with his party's rank and file.

Cameron and Osborne too must surely know how damaged their modernisation project would be if they cave in to BAA's lobbyists on this. Today Osborne's office has told the FT there's "no softening on the question of Heathrow" - something reiterated too by Greening's spokesperson. So for now at least, the third runway has not come back from the dead - and as Paul Goodman has commented - it remains unlikely to do so.

But whatever happens on Heathrow, the Prime Minister and the Chancellor have already made clear they do want new runway capacity in the South East. That suggests they do plan to U-turn on their coalition agreement commitment not to approve new runways at Gatwick, Stansted or Heathrow. A Lib Dem source signalled to the Telegraph that whilst they're opposed to a new runway at Heathrow, they too are open to expansion somewhere else.

Since aviation remains the fastest growing cause of climate change, and millions of people living under flight paths would be blighted by noise and air pollution, we could yet see seasoned environmentalists once again arm-in-arm with Middle England rising up to stop the aviation juggernaut from destroying the places people love and undermining our efforts to curb global warming.

If this happens, the Chancellor will have created a political nightmare because of his starry-eyed devotion to corporate lobbyists. Sound familiar?

Joss Garman is a senior campaigner at Greenpeace UK. He previously co-founded the Plane Stupid direct action campaign against airport expansion. Follow him on Twitter: @jossgarman