Plans to expand Heathrow with a third runway earmarked by former PM Sir Keir Starmer as 'a cornerstone of delivering economic growth' have been delayed and still face a battle to succeed.

The expected 2035 project completion deadline was postponed after chiefs at the London airport told ministers it was always 'too ambitious'.

The airport expansion could also prove a sticky topic for the new Prime Minister Andy Burnham as he heads to his first party conference as PM and Labour leader.

He criticised the plans which have the full support of his Chancellor John Healey when he was Manchester Mayor.

The PM is said to have told Labour colleagues that he had 'never been in favour' of the scheme to build a third runway. 

And while he is said to be more 'open minded now' he said yesterday on ITV's Lorraine Kelly show that the views of Londoners must come first and it was the 'voice of local areas that must be heard first in this debate before anywhere else'.

Former Chancellor Rachel Reeves championed the £49billion project as a cornerstone of her plans to boost the economy in 2025 claiming it would be up and running in a decade and create 100,000 jobs.

She set herself up as a key supporter of a third runway when she said in January 2025 that it would 'unlock further growth, boost investment, increase exports, and make the UK more open and more connected'.

 Meanwhile her successor Mr Healey has also nailed his colours to the mast, saying: '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.'

But Heathrow, which lost its moniker as the world's busiest airport just this summer to Istanbul, confirmed today that they will instead be focusing on securing planning permissions by 2029 with a runway then possible by 2039.

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

Plans to build a third runway at Heathrow have been mooted for the last 80 years, first surfacing as far back as 1946 in the post-war period.

But they have been continually thwarted by indecisive politicians and stiff opposition to the project from campaigners and environmentalists.

Senior Labour figures including London Mayor Sir Sadiq Khan – who described it as an outdated risk 'we simply cannot afford to take' – and Foreign Secretary Ed Miliband – who raised fears about global warming – are among hardline critics of the expansion.

Mr Burnham has a record of attacks on the proposal going back years. In January last year the then-Manchester mayor branded it a 'model for an ever-overheating UK economy', warning it could not come at the 'expense of essential investment in northern infrastructure'.

In 2018 he said: 'I'm against a third runway at Heathrow because of the need to limit national levels of aviation We should use spare capacity at Manchester and Birmingham instead.'

The following year he warned that the expansion would 'trap infrastructure spending inside the M25 for 10 years'.    

Many have argued that not only would it have severe impacts on the environment but also that that could be for very little real economic benefit once the huge costs of any such project were taken into consideration.

There was also a dispute on who should build any new runway with a rival scheme to the official Heathrow plan which would not involve moving a section of the M25 proposed by billionaire airport hotel magnate Surinder Arora.

Meanwhile, while the row rumbles on, other airports worldwide have been constructed from scratch or have expanded rapidly including Beijing Daxing International airport, which operates four runways, built in just five years between 2014 and 2019.

A consultation was finally launched on the draft Heathrow Expansion National Policy Statement this June and closed at the beginning of this month.

Once responses are analysed, a finalised version is likely to be put to what will probably be a delayed vote in Parliament in January 2027. It was originally planned for this autumn.

If it is passed, a tender stage may see Mr Arora, worth an estimated £1.7billion, go head to head with Heathrow, with a final decision in the hands of the Transport Secretary.

It is also widely expected that environmental campaigners will launch a legal fight to block final expansion plans.

But Gary Smith, General Secretary of the GMB, said it was time 'to put an end to decades of talk and lost benefits for working people across the country' and 'get cracking'.

'Securing a deliverable, workable and practical delivery timeline for Heathrow expansion, that unlocks over 100,000 jobs, is paramount,' he told today's Times.

A spokesman for Heathrow defended setting 'ambitious targets' saying they had always focused on securing planning by 2029 and said 'the sooner expansion begins, the sooner the whole UK will benefit.'

'This is a national project, 100 per cent privately financed, which will support growth today and secure the UK's position in the global economy once the runway opens,' they added.

A Department for Transport spokesman said the timeline had always been 'ambitious' and they would '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'.

They confirmed that a formal planning application had not been submitted yet and said they could not comment on 'ongoing consultation processes or prejudice them in a way that will only delay progress'.