Conservative supporters of a third runway at Heathrow will pay a price with voters during the next general election campaign, Zac Goldsmith has warned.
The Tory member for Richmond Park and North Kingston has promised to resign, triggering a by-election, if David Cameron bows to pressures from within his own party to change his party's opposition to further expansion at Heathrow.
Two-and-a-half years later his pledge looks in danger of being broken, as calls for a third runway attract growing support from Tory backbenchers. Chancellor George Osborne is thought to back revisiting the issue, which is expected to become the subject of a delayed consultation on Britain's aviation strategy expected this autumn.
"We're living in a time where people's faith in politics and trust in politicians has probably never been lower," Goldsmith told politics.co.uk.
"I think that's a dangerous position to be in, where the breakdown is almost complete. When politicians casually break unambiguous pre-election promises, voters remember that. People will rightly ask themselves: what in an election manifesto can we believe?"
The Conservatives' 2010 manifesto stated that the party's goal was to "make Heathrow airport better, not bigger". Leaflets promised "no ifs, no buts, no third runway". But not all of the party's MPs agreed with the policy.
Elizabeth Truss, the convenor of the Tories' Free Enterprise Group, wants to avoid the 'stopgap' accusation by increasing Heathrow's size to not three but four runways.
"I think that on existing evidence Heathrow is the best option because it is the hub airport at the moment, and there would be a huge amount of cost in moving it elsewhere," she argued in an interview for a politics.co.uk feature on the third runway issue.
Truss is more relaxed about the Tories' manifesto commitment. She pointed out this was to not build a third runway in the current parliament.
"Yes, we stood on that manifesto. It's in the coalition agreement. But I think we're looking at anything happening in terms of tarmac after that period," she argued.
"This isn't going to happen before 2015. What we're talking about is giving people confidence in the future of Britain's economy."
Goldsmith warned that Tory MPs who went against the party's policy would find themselves struggling to win over voters' trust at the next election, however.
He predicted it will "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".
Reopening the third runway debate is likely to stoke tensions with the Liberal Democrats, who remain opposed to a third runway at Heathrow. The party will debate a policy motion at their party conference in September ruling out any new runways at Heathrow, Gatwick or Stansted.
"With Birmingham looking to expand, Stansted only half full and Gatwick expanding into emerging markets, regional airports and other airports within London can meet demand for the short to medium term," transport spokesman Julian Huppert argued. "Especially if we provide them with the transport links they so desperately need."
Goldsmith said he hoped Britain could adopt a twin-hub approach, with Heathrow serving western destinations and Stansted developed as an eastern-facing hub. This would require improved rail links to the Essex airport but would cost "considerably less money" than the alternatives, he suggested.
Labour criticised the coalition for being so divided on the issue. The opposition is calling for cross-party talks to secure a consensus that will last beyond the next general election.
"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," shadow transport secretary Maria Eagle told politics.co.uk.
"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?"
Labour faces divisions of its own over the third runway issue, however. Earlier this week former chancellor Alistair Darling called for the party to resume its support of a third runway at Heathrow.