The government postponed giving the go-ahead to a third runway at Heathrow yesterday amid growing pressure to reverse its support for expansion.

Transport secretary Geoff Hoon announced a delay in his decision on whether to expand Heathrow until the end of January, saying he needed more time to reach “the right conclusion”. Hoon has repeatedly signalled he supports a third runway in line with predecessor Ruth Kelly. He had been due to make public his decision within days.

The government has already delayed the announcement twice – having previously signalled a decision would be made before the summer and then in the early autumn before pushing it back to December.

Hoon said yesterday: “There are strong views across a range of interests.”

However, he added: “The government set out its position in 2003 that we are in favour of the extension.”

At least five government ministers oppose expansion and a growing number of Labour MPs are against. The Conservatives have repeatedly said they would cancel plans for a third runway on forming a government and many Labour MPs fear local opposition to Heathrow expansion would cost the party seats at a general election. A parliamentary vote on the issue would almost certainly see the government defeated.

It is understood the new energy and climate change minister Ed Miliband persuaded Hoon to look again at the proposals, which would see construction of a third runway by 2020 as well as greater use of the existing runways. An additional runway would increase flights in and out of Heathrow from 480,000 to 700,000 a year.

Airlines and airport operator BAA expressed a lack of concern about the delay, remaining confident Hoon supports expansion. Airport Operators Association chairman Ed Anderson described the delay as “entirely reasonable”. However, Greenpeace suggested “pro-runway” supporters in the government are in retreat.