Prime Minister Andy Burnham has cast fresh doubt over Heathrow’s plans for a third runway, putting him at odds with Chancellor John Healey, who has given the £49 billion project his full backing.

The planned expansion would increase Heathrow’s capacity to up to 756,000 flights and 150 million passengers a year.

Mr Healey has insisted the economic case for expansion “stacks up”, arguing that a third runway is vital to driving national economic growth.

Mr Burnham, however, struck a more cautious note when speaking to ITV London on Friday, stressing that the views of Londoners must come first.

“It's the voice of local areas first that must be heard. London needs to be heard first in this debate before anywhere else.”

The Prime Minister said the consultation, which has just ended, would be “considered carefully”.

Asked if he was “not keen” on the project, Mr Burnham stopped short of offering his full support.

“It’s not a case of not keen,” he said. “We need to look at what people have said, and it's for London to come forward with its majority voice first and foremost.”

The comments put Mr Burnham at some distance from Mr Healey, MP for Rawmarsh and Conisbrough in South Yorkshire, who has thrown his full support behind expanding the west London airport, as his predecessor Rachel Reeves had done.

Speaking in the House of Commons, Mr Healey said: “After years of delay, years of indecision, years of often vexatious challenge, we have given the go-ahead to this project quite simply because the economic case stacks up and will help bring growth.”

Mr Healey’s position is clear, but he is not the only Cabinet minister to have faced questions over the expansion.

Foreign Secretary Ed Miliband has previously raised objections to a third runway and its impact on global warming.

Annual figures from trade body Airports Council International show Heathrow was Europe’s busiest airport from 1996 to 2019.

It lost that position in 2020 amid coronavirus travel restrictions before regaining it in 2023 and holding the title since then.

In 2025, the airport recorded 84.46 million passengers.

A public consultation on the Government’s Heathrow expansion national policy statement closed on September 1.

A formal planning application has not yet been submitted.