The Labour Party played down reports last night that leader Ed Milliband is set to abandon his opposition to a third runway at Heathrow.

But he is under pressure from shadow chancellor Ed Balls to be more supportive when the Davies Commission reports next week, the Guardian reported.

The prospect of political assent for a third or fourth runway at Heathrow appeared to increase further, ahead of next week’s interim report from commission chairman Sir Howard Davies which is set to announce a shortlist of options for expansion in the southeast of England.

According to one source, an early draft had Heathrow at the centre of the commission’s thinking, with options for a third or fourth runway at the west London hub, and potentially additional capacity at Gatwick.

Shadow transport secretary Mary Creagh has tried to be non-committal towards the commission, 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. Obviously the Conservatives and Lib Dems haven’t made any such commitments.”

Labour would not rule any runway options in or out while the Davies Commission was still deliberating, she added.

While Miliband was a minister in the last Labour government that approved plans for a third runway at Heathrow, his concerns were well established, the newspaper reported.

At one point he threatened to resign as energy secretary if Heathrow was granted a third runway, citing the effect on carbon emissions, and as leader he ruled out the party standing by its former policy after the coalition scrapped the runway in 2010.