Andy Burnham refused five times to back a third runway at Heathrow in an interview on Sunday, casting massive doubt on the future of the controversial project.

The Prime Minister stressed that key to supporting the scheme was the view of London. Mayor Lord Sadiq Khan vehemently opposed to a bigger Heathrow.

Mr Burnham’s stance is also in marked contrast to that of his Chancellor John Healey who just weeks ago gave firm backing to expansion of the west London airport.

The PM’s intervention comes as the £49billion development, which airlines say would be the most expensive new runway project ever and would involve moving the M25, has already been hit with years of delays.

Appearing on the BBC’s Sunday with Laura Kuenssberg show, Mr Burnham was asked: “Building another runway Heathrow seems to have been delayed.

“Rachel Reeves used to say that would bring billions of extra pounds to the economy. Are you going to back another runway at Heathrow?

The PM responded: “Well, there's been a consultation on it...”

He was pressed: “Are you going to back it?”

Mr Burnham replied: “It's a contested issue, isn't it?”

But he was again asked: “Are you going to back it.”

The Prime Minister stated: “I think, principally, it's a matter for London.”

But Ms Kuenssberg questioned: “There's a vote in Parliament. You're the Prime Minister. Are you going to back it or not?

The Prime Minister came back: “Well, I think you've got to hear the voice of people there first. It's not right for me to just jump straight in on the back of the consultation.”

But he was asked: “No one's jumping straight in through this debate. It's been going on for decades. No one's jumping straight in.”

The PM said: “I think it’s right that we hear what people have said through the consultation and then consider the way forward from there.”

He was again pressed: “That sounds like you are not up for it because the London mayor Sadiq Khan isn't that up for it.”

The premier said: “There's a consultation, but there are different views, and you have to take those views seriously in coming to a decision.“

Mr Burnham has previously expressed doubts on the project, arguing it will divert much-needed development funds from the North.

The new runway would increase the west London airport’s capacity to 756,000 flights and 150 million passengers a year.

Green Party leader Zack Polanski has branded a third runway a “great betrayal”, arguing that it is a “betrayal of climate commitments, betrayal of communities breathing polluted air, and betrayal of our children’s future”.

Mr Polanski hit out after the Government’s own global warming advisers warned that there is “no credible pathway” for a Heathrow third runway within the UK’s legally-binding climate targets under current policies for cutting aviation emissions.

The UK’s Climate Change Committee (CCC) also stressed that the Government “does not have a credible plan to reduce” aviation emissions, posing a serious challenge to meeting overall global warming targets.

Business leaders in London, though, support a third runway.

Ed Richardson, programme director for Transport at BusinessLDN, said: “Heathrow’s third runway would provide an immediate boost to the economy through tens of billions of private investment, which would benefit a supply chain spanning the UK.”

Following Mr Burnham’s comments, a Heathrow spokesperson said “We agree with the Prime Minister that local voices must be heard. We know from consistent polling over the last decade that communities support our plans for expansion, and support is only growing over time.

“But critically, expanding Heathrow is a national project which will create jobs and boost growth in every part of the country.

“That’s why it is supported by trade unions, business groups, airports and communities across the UK and why we need to crack on with delivering it as quickly as possible.”