David Cameron faces a backbench rebellion over the Conservative Party's opposition to a third runway at Heathrow airport, as a number of senior opposition figures voice support for the £9bn expansion plan.
The Conservatives have called a Commons vote, which will not be binding on the Government, for next Wednesday. They hope to embarrass Labour by exposing the number of Labour MPs who are willing to vote against the Government's support for the new runway.
Some potential Labour rebels will now support the Government after it abandoned an immediate increase in flights and made environmental concessions. Meanwhile, disquiet grows among Tory backbenchers over the fierce opposition to aviation expansion voiced by the shadow Transport Secretary, Theresa Villiers.
Several Tory frontbenchers also have misgivings about Ms Villiers' remarks. The shadow Commons Leader, Alan Duncan, and the newly appointed shadow Home Secretary, Chris Grayling, are said to have privately voiced concerns over the party's opposition to expansion over Heathrow. The shadow Chief Secretary to the Treasury, Philip Hammond, is also said to have shared those anxieties until recently.
The Shadow Cabinet has been given stern orders not to question publicly the party's position, which the leadership believes will be popular with voters.
One of the backbenchers fronting calls for the party to support expansion, David Wilshire, the MP for Spelthorne in Surrey, has met Mr Cameron and Ms Villiers to try to change the party's position. He has promised not to start a high-profile campaign.
"Provided that the environmental conditions can be met, which the Government has introduced, expansion should be supported," he said.
Mr Wilshire will ensure, along with the other leading pro-expansion Tory MP Ian Taylor, that he is not in the chamber when the vote takes place on Wednesday. The number of Tories planning to abstain or vote with the Government is said to be well into double figures, which should help the Government win the vote narrowly.
Peter Lilley, a former trade and industry secretary under John Major, also said he supported expansion of aviation at Heathrow and would consider voting with the Government. "It makes sense to have a hub airport in one place. I will need convincing from Theresa that our position is coherent," he said.
Mr Lilley also said that he supported Boris Johnson's idea of building a new airport in the Thames estuary, after visiting a similar island airport in Hong Kong in 1999 that had been planned while he was trade and industry secretary. "It showed me that it can be done and the economics are not totally out of the question," he said.
The former Shadow Cabinet minister Ann Widdecombe has also criticised her own party's position: "Heathrow is a very successful airport and it seems there is a pressing need to expand it."
Philip Davies, the MP for Shipley, said: "It is a very finely balanced issue as ever between business and the economy, but ultimately I would come down in support of a third runway."
The party leadership hopes to use the vote to call the bluff of some of its MPs who are considering voting for a third runway. A source said: "It is a good chance for the Conservative rebels to show if they have the courage of their convictions."Reuse content