The political fallout from a U-turn on Heathrow

For Zac Goldsmith, Conservative MP for Richmond Park & North Kingston and staunch opponent of Heathrow expansion, it would be an “off-the-scale betrayal” for David Cameron to back a third runway.

Mr Goldsmith said the prime minister had made “as clear a promise as a political promise can be” to voters while on the campaign trail before the 2010 election.

He has emerged as a leading Conservative critic of expanding Heathrow along with the mayor of London, Boris Johnson, and has been outspoken in his criticism of Chancellor George Osborne – a supporter of a third runway somewhere in the south east.

The transport secretary, Patrick McLoughlin, said the government was now not ruling out a third runway – one of the options shortlisted in Sir Howard Davies’s interim report on airports today.

But the fact that a decision will not be taken until 2015 means the prime minister cannot be accused of performing a U-turn, Mr McLoughlin insisted.

He told the BBC’s Andrew Marr show: “What we said at the last general election was that we would not build a third runway in this parliament. We will not be building a third runway in this parliament. We will stick by our manifesto commitment.”

In fact the Conservatives’ manifesto of 2010 does not contain any time references. It simply states: “We will stop the third runway and instead link Heathrow directly to our high speed rail network, providing an alternative to thousands of flights.

“In addition, we will block plans for second runways at Stansted and Gatwick.”

‘No ifs, no buts’

In 2009, as reported in the local press, Mr Cameron told voters in Richmond: “The third runway at Heathrow is not going ahead, no ifs, no buts.” Again, there was no reference to 2015.

In March 2010, just before the election, he was quoted by the Independent as saying: “I have made it very clear time and again that under a Conservative government the third runway is not going ahead: no ifs, no buts.”

Of course the Conservatives did not win an outright majority, but they were at one with the Lib Dems on the issue, and the coalition agreement said: “We will cancel the third runway at Heathrow. We will refuse permission for additional runways at Gatwick and Stansted.”

Against ‘unconstrained expansion’

Neither Mr Cameron nor the Liberal Democrat leader, Nick Clegg, have commented directly on today’s Airport Commission report.

Mr Clegg was equivocal about the options for future airport expansion in an interview last year, saying: “There are lots of ideas. What we need to do as a government is sensibly say we are going to stick to our coalition agreement but we are not sticking our heads in the sand. We recognise it is an issue.”

Ed Miliband’s record on Heathrow is more difficult to pin down, although he it was widely reported that the Labour leader was a leading critic of the policy when his party adopted it in 2009.

The then secretary of state for energy and climate change was understood to have blocked the party’s adoption of the policy before falling into line at the eleventh hour in exchange for new measures on tackling aviation emissions.

Mr Miliband did not speak openly of his misgivings about a third runway but said afterwards: “I was not in favour of unconstrained aviation expansion, because we need to understand the climate change challenge that we face.”

Resignations and reshuffles

Both Labour and the Conservatives are split on Heathrow, with cabinet and shadow cabinet members at loggerheads over the issue.

Frontbencher Justine Greening is considered an implacable opponent of a third runway. She campaiged for re-election in her west London Putney constituency on the issue and used Mr Cameron’s “no ifs, no buts” slogan in her election material.

Ms Greening’s exit from the Department of Transport last year was widely interpreted as a sign that the government’s position on Heathrow was softening.

In an interview with the BBC’s Today programme last year she said “it would be very difficult” for here to remain in the cabinet if the government backed plans to expand the airport.

‘Off the agenda’

Mr Goldsmith has gone further, repeatedly promising to trigger a by-election if the Conservatives carry out what he considers to be a catastrophic U-turn, and giving local voters the chance to penalise the party.

Labour was also reported to have reshuffled its front bench with Heathrow in mind when it swapped shadow transport secretary Maria Eagle, an apparent opponent, for Mary Creagh.

In 2011 Ms Eagle was saying: “The answer for the south-east is not going to be to fall back on the proposed third runway at Heathrow. The local environmental impact means that this is off the agenda.”

Labour’s stance is now much more equivocal, with Ms Creagh saying: “No party can say now that it will implement its recommendations when we simply don’t know what the costs of any proposals will be.”

The shadow chancellor Ed Balls, let slip his support for a third runway in a recent Times interview, saying he would prefer that option over the High Speed 2 rail network.

His predecessor, former chancellor Alistair Darling, has called for a third runway to be built now.