But airport bosses admitted the deadline for planning permission was 2029, with the runway opened “within a decade” – effectively pushing the project back to 2039.

Now, the airport expansion may not go ahead at all.

Mr Burnham met with Transport Secretary Heidi Alexander last week to discuss the Government’s position on the Heathrow project.

He was “unconvinced” by the need for a third runway, given recent approval of expansion programmes to Gatwick, Luton, Stansted, and London City, according to The Sunday Times.

Sources told the newspaper he also pointed to a £2billion investment being made at Birmingham airport announced last week.

Downing Street sources insist Mr Burnham did not give a “firm no” to the third runway and remains “open-minded” to the expansion’s benefits.

The Prime Minister, last month, refused to back the London infrastructure project when directly asked.

He said: “I think principally, it’s a matter for London and Londoners.”

He added: “I think we ought 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.”

Labour opponents of the expansion scheme include Foreign Secretary Ed Miliband and Mayor of London Lord Khan.

The Climate Change Committee, the Government’s official advisory group, said the third runway was not “currently compatible” with Net Zero targets last month.

But the Transport Secretary said the carbon impact of an increase could be offset “holistically” elsewhere.

Reform UK said the delay was a sign of “third-world decline”, while the Conservatives vowed to ‘sweep away the blockers’ preventing expansion.

On social media, Nigel Farage said: “Heathrow’s third runway will now be delayed until 2039. China has built more than 100 airports in the last 25 years.

“Britain is truly a broken country, we can’t build or do anything. Only Reform will reverse our third-world decline.”

Conservative Shadow Chancellor Andrew Griffith at his party’s conference said the Tories would do “whatever it takes to end the delays and boost capacity by backing the third runway”.

A Department for Transport spokesman, reacting to the delay, previously said: “There is currently no live planning application for a third runway, and we cannot comment on ongoing consultation processes or prejudice them in a way that will only delay progress.

“The timeline has always been ambitious.

“We’ll continue to work with promoters, including Heathrow, and all other stakeholders at pace to ensure the right framework is in place for which a planning application for a third runway could be considered.”

Heathrow Third Runway Cast into Doubt as Andy Burnham Remains ‘Unconvinced’

Plans to build a third runway at Heathrow Airport have been thrown into fresh uncertainty after Prime Minister Andy Burnham declined to give the multibillion-pound project his unequivocal backing. The hesitation has raised questions about whether one of Britain’s most ambitious infrastructure schemes can move forward on schedule, with airport executives warning that investors will not wait indefinitely for political clarity.

Heathrow’s proposed expansion, estimated to cost £33 billion, has been promoted by supporters as a major investment in Britain’s economic future. Yet the project faces mounting challenges, including political disagreement, environmental concerns, planning hurdles and uncertainty over its financial returns.

The immediate concern is Burnham’s reluctance to endorse the proposal. While the Labour government previously supported airport expansion as part of its economic growth strategy, the prime minister has argued that the issue requires careful consideration because it remains the subject of consultation and potential planning decisions.

His position has placed the project at a critical juncture. Heathrow’s chief executive, Thomas Woldbye, has warned that the airport’s investors will reassess their plans if the government does not provide greater certainty by the end of 2026. The decision could determine whether the project progresses towards a formal planning application or faces another period of delay.

For supporters, a third runway represents an opportunity to strengthen Britain’s international connections and expand the capacity of its busiest airport. For opponents, it raises serious questions about carbon emissions, noise, congestion and whether the economic benefits justify the scale of the investment.

The disagreement now places Burnham under pressure to explain how his government intends to balance economic growth with environmental commitments and the concerns of communities affected by airport expansion.