The first sign of a government retreat on airport expansion came yesterday with the announcement that a decision on whether to build a new runway at Heathrow would be delayed until the end of January.

Three weeks ago Geoff Hoon, the Transport Secretary, told the House of Commons that he would publish his decision by Christmas.

Yesterday, however, he claimed that he needed more time to consider the 70,000 responses to the Government’s consultation on its proposals for a third runway, sixth terminal and 220,000 more flights a year.

The consultation closed in February and the Department for Transport has been analysing the responses for more than nine months.

Mr Hoon said that, in the two months since taking up his appointment, he had been able to “begin considering the evidence”.

Senior aviation industry figures privately expressed concern that he was preparing to change the Government’s position. Mr Hoon is unlikely to rule out expansion, but may order another assessment of Britain’s need for more airport capacity in the light of rising concern about climate change, the recent downturn in demand for air travel and the impending break-up of BAA, which owns Heathrow, Gatwick and Stansted.

Ed Miliband, the Energy and Climate Change Secretary, is the most influential of a group of Cabinet ministers who believe privately that a new runway is incompatible with the Government’s commitment to cut carbon dioxide emissions by 80 per cent by 2050.

Hilary Benn, the Environment Secretary, Harriet Harman, the Leader of the Commons, and David Miliband, the Foreign Secretary, have also expressed doubts about whether the economic benefits of the runway would justify the extra three million tonnes of CO2 that would be emitted each year from the increase in air travel.

Almost 60 Labour MPs have signed a Commons motion calling on the Government to “rethink its plans for a third runway at Heathrow”.

In September the Conservatives said they would cancel the third runway and build a high-speed railway line instead. The Liberal Democrats also oppose the runway It would create new flight paths over a million homes and that could cost Labour up to a dozen seats in West London and Berkshire at the next election.

A senior airline source said: “Gordon Brown has strongly supported the runway since 2002 but we fear that, at the last minute, he has lost his nerve and been persuaded by the Milibands to think again.”

BAA was still confident yesterday that it would eventually get permission for the new runway. A spokesman said: “Given the complexity of the issues involved, we understand why the Government is taking further time to consider these matters.”

On Tuesday Jim Fitzpatrick, the Aviation Minister, told an airline conference: “Unless Heathrow benefits from additional capacity, the inevitable result would be the loss of flights to airports like Frankfurt, Paris Charles de Gaulle and Schiphol – which still have the room to grow.”

He said that this sentence in his speech had been specifically approved after he had queried it with advisers.

In a written statement, Mr Hoon said: “I share the desire on all sides of the House, and among the wider public, for this issue to be resolved. I am equally aware of the importance of reaching the right conclusion.

“I know that there are strong views across a range of interests. I will ensure that I give proper consideration to the evidence before me.”

Theresa Villiers, the Shadow Transport Secretary, said: “Opposition to a third runway is gathering momentum every day. I suspect this postponement is an indication that Gordon Brown is finally starting to realise that he is on the wrong side of the debate.”

British Airways said: “We had hoped for a decision before Christmas. However, having waited six years to reach this point, we can afford to wait a little bit longer.”

John Sauven, director of Greenpeace, said: “As the recession bites and airlines go bust or cancel routes, the last thing Britain needs is extra runway capacity. Instead we need investment in the railways to replace short-haul flights and cut pollution.”

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