David Cameron's speech yesterday outlining a Blue/Green charter may prove of greater significance than some in the industry would wish.
Cameron called Gordon Brown's commitment to expanding Heathrow "pig-headed" and questioned the economic justification for a third runway in terms that go some way to boxing him in on the issue.
The Tory leader realised some time ago he could outflank the Government on the environment and has shown a willingness to alienate business interests in doing so. But yesterday could mark a step-change - although politicians' speeches must be seen in the context of those they were addressing, and Cameron was speaking to an environmental audience.
Nonetheless, he called into question the economic argument that is the bedrock of the case for Heathrow expansion. "There are increasing grounds to believe the economic case for a third runway is flawed," he said. "Why are they hell-bent on pressing ahead without a rigorous analysis of whether we need it? The priority for Heathrow is making it better, not bigger."
BAA and BA, which would benefit most from Heathrow's expansion, must be wringing their hands and reaching for the phone numbers of their hardest-hitting lobby groups. They believed they had a third runway in the bag, with Gordon Brown and transport secretary Ruth Kelly on board and a green light expected in the autumn.
Cameron went further, implicitly attacking those in industry who have called for a retreat on moves toward carbon-related taxes or a more costly emissions trading scheme when the oil price is so high. Insisting he wanted to make his position "absolutely clear", Cameron said: "We are not going to drop the environmental agenda in an economic downturn. . . Those who say, 'Tough emissions targets will damage our industry' have got it exactly wrong."
Heathrow has the potential to become a major political football. Brown is wounded - probably fatally - and opposition to his Government is growing. Heathrow expansion can rally opponents across party lines and many of those lobbying for it are hardly popular in public eyes.
In practice, Cameron would probably sign off airport expansion plans. He made no criticism yesterday of expanding Heathrow through mixed use of existing runways or of building runways elsewhere. And making a statement in opposition is a far cry from implementing it in government.
But the process of building a runway takes time - the best estimate at Heathrow is by 2018 - and unless something remarkable happens, Cameron is likely to be in Number 10 in less than two years.
Assuming the DfT gives its blessing to a third runway as expected later this year, would the first Tory prime minister in 13 years really cancel it? Or might he say the development was too advanced to cancel or the situation had changed or the decision required an independent review?
There are many ways to retreat on a pre-election promise. Yet between then and now a head of steam can build that changes the ground on which decisions will be made. The clouds are darkening for supporters of expansion.
You can read Cameron's speech at: http://www.conservatives.com/tile.do?def=news.story.page&obj_id=145279