Heathrow’s third runway has been delayed for four years until 2039.

Bosses at the airport, the largest and busiest in the UK, have told the Government that sticking to the current 2035 deadline is not possible, it is understood.

The shifting deadline is likely to come as a blow to Andy Burnham’s ambitions to deliver economic growth, as Labour’s annual conference kicks off in Liverpool.

The 2035 deadline was set by then-chancellor Rachel Reeves last January, and was considered an ambitious goal at the time.

Ms Reeves used a major speech on infrastructure to announce the Government would be supporting the third runway project as a means of growing the economy, and also said it would create 100,000 jobs.

The airport aims to get planning permission by 2029, and has from the start considered building the new runway within a decade to be a reasonable goal.

Its bosses believe it could be delivered more quickly, but that this may require further regulatory red tape to be removed beyond reforms that the Government has already made to planning law.

A Heathrow spokesperson said: “It’s right that ambitious targets were set; the sooner expansion begins, the sooner the whole UK will benefit. Our focus has always been to secure planning permission by 2029.

“Once achieved, the runway will be open within a decade – and the benefits of expansion can be felt from today. At least 108,000 new jobs and billions invested in supply chains in every part of the country.

“This is a national project, 100% privately financed, which will support growth today and secure the UK’s position in the global economy once the runway opens.”

A Department for Transport spokesperson 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.”

Transport Secretary Heidi Alexander insisted the project could go ahead in a way that would not fall foul of climate change commitments.

The Climate Change Committee, the expert panel that advises the Government, said earlier this month the expansion of Heathrow airport cannot go ahead unless the aviation industry is forced to clean up its emissions.

The cost of international flights might have to increase by hundreds of pounds by 2050 to pay for measures that will help the airline sector cut its carbon pollution to zero overall, known as net zero, the committee said.

Ms Alexander told the Daily Telegraph the committee had set out “one view” but there was “more than one pathway to meeting our climate mate change obligations”.

“We do remain committed to net zero, and we’re updating some of our wider decarbonisation plans in transport as well,” she said.

“But the UK’s climate change targets are ultimately economy-wide targets, and we really need to look holistically at how emissions are reduced across the economy as a whole.”

She said an expanded Heathrow could be “the country’s front door” to tourists from China and India.