Heathrow Airport's proposed third runway has been delayed by four years, pushing the expected opening date back to 2039.

Airport bosses have told ministers that the previous 2035 target is simply not possible, describing the timeline as unrealistic. That original 10-year goal was backed last year by former Chancellor Rachel Reeves alongside Sir Keir Starmer, with Ms Reeves promoting a £49billion plan on the basis that it would create 100,000 jobs and significantly boost the national economy.

Under the updated timetable, the London airport aims to submit a formal planning application for the expansion by 2029. Airport leadership maintains that delivering the runway within a decade of planning approval remains a reasonable target, though they have indicated the build could be expedited if the Government removes additional regulatory red tape beyond existing planning reforms.

A Heathrow spokesman defended the updated schedule, saying: "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 per cent privately financed, which will support growth today and secure the UK’s position in the global economy once the runway opens."

The project faces a changing political landscape following Andy Burnham's succession to No 10. The Prime Minister has not publicly addressed the airport's expansion since taking office, and it is understood he has previously told MPs he was against the investment on the grounds that funding and focus could be allocated to other regions.

Opposition on the ground remains strong, with local resident groups warning the extra flights will drive up emissions and noise pollution. London Mayor Sir Sadiq Khan has also raised questions over the project, warning that expanding capacity would put the health of Londoners at risk.

Environmental scrutiny has intensified following a warning last week from the Climate Change Committee, the Government's official advisory body. It stated that the third runway is not "currently compatible" with Net Zero targets, adding that meeting 2050 climate goals would require airlines to enforce carbon offsets that could add an extra £400 to the price of a transatlantic flight.

Transport Secretary Heidi Alexander has rejected that assessment, insisting the expansion is compatible with Net Zero because emissions increases could be offset "holistically" elsewhere. Writing in the Telegraph, Ms Alexander argued the project will generate thousands of jobs and serve as "the country's front door" to visitors from India and China. Chancellor John Healey also reaffirmed Government backing earlier this month, citing the need to move past "years of indecision and years of often vexatious challenge... because the economic case stacks up and will help bring growth."

A Department for Transport spokesman said there is currently no live planning application in place, noting that the overall timeline has always been ambitious and that officials will continue working alongside Heathrow and other stakeholders to establish the necessary framework. Meanwhile, Reform UK leader Nigel Farage criticised the delay on X, calling the setback a sign of "third world decline" and pointing to airport construction rates in China.

Runway expansion plans at Heathrow first surfaced back in 2009, but they have faced repeated delays across successive governments. What we do not know yet is whether ministers will agree to strip away the further regulatory rules Heathrow says are necessary to speed up delivery once 2029 arrives. I'll be following this one — check back for updates.