Heathrow Warns Third Runway Could Slip to 2039 as Planning Delays Mount

Heathrow Airport has cautioned that its long-planned third runway may not become operational until 2039, a four-year slip from the timeline the UK government had been aiming for. The airport blamed the potential delay on persistent planning and regulatory hurdles, warning that the 2035 target is becoming increasingly hard to meet unless the process is simplified.

The government had set its hopes on the new runway opening by 2035, with the project carrying an estimated price tag of £49bn. Heathrow now says its "core scenario" has always been to open a new runway within a decade of securing planning permission, which it hopes to obtain by 2029. That calculation points to a possible opening around 2039 rather than the mid-2030s.

The Department for Transport (DfT) acknowledged the difficulty of the original schedule, noting that the timeline had "always been ambitious." A department spokesperson said officials would keep working with promoters, including Heathrow, and other stakeholders "at pace" to ensure the right framework is in place for a planning application to be considered.

The DfT also confirmed that no live planning application for a third runway currently exists, and declined to comment on ongoing consultation processes for fear of prejudicing them in a way that might only slow progress further. That admission underscores how early the project still is in the formal approvals process, despite years of political debate.

Heathrow said it was encouraged by the chancellor's efforts to streamline infrastructure delivery and remove policy and regulatory bottlenecks. The airport promised to continue working with ministers, airlines and stakeholders to "progress the planning application with pace," framing the project as a national priority that is 100% privately financed.

The expansion debate dates back well before the current government. Former chancellor Rachel Reeves announced the government's backing for the project in January 2025. Prime Minister Andy Burnham, who had previously been critical of the scheme, said he was "open-minded" about it when he took office.

Supporters argue the runway would deliver a significant economic boost, including around 100,000 jobs. Heathrow's own spokesperson put the figure at "at least 108,000 new jobs," alongside billions of pounds invested in supply chains across every part of the country. They described it as a national project that would support growth now and secure the UK's position in the global economy once the runway opens.

Opposition has been wide and sustained, drawing in environmental campaigners and resident groups from neighbouring areas. London Mayor Sadiq Khan has consistently opposed the expansion, warning about its impact on noise, air pollution and climate change. The project's critics argue the costs and environmental harm outweigh the promised economic gains.

The physical scale of the build is substantial. Hundreds of homes would need to be demolished, rivers diverted, and the M25 motorway rerouted between junctions 14 and 15 through a tunnel beneath the new runway. Such works would reshape swathes of west London and the surrounding motorway network, adding to the complexity of both planning and construction.

Flight capacity would rise sharply if the runway is built. The airport is currently capped at 480,000 flights a year, but that figure could increase to 720,000 — an average of nearly 2,000 flights a day. That expansion is central to Heathrow's argument that it needs a third runway to remain competitive as a global hub.

A consultation on the expansion was published in June this year. Once finalised, the plans must be put to a parliamentary vote, which could reportedly be delayed until 2027. That parliamentary stage represents another potential bottleneck, sitting between the consultation and any formal planning decision.

Heathrow remains the UK's busiest airport, handling more than 80 million travellers annually through its four passenger terminals and two runways in west London. Its current configuration has been operating near capacity for years, which is why the third runway has been a recurring flashpoint in British infrastructure policy.

The latest warning effectively shifts the burden of urgency onto the government. Heathrow's position is that ambitious targets were rightly set, and that the sooner expansion begins, the sooner the country benefits. But without faster planning reform, the airport suggests, the gap between political ambition and shovels in the ground will keep widening.

For the government, the choice is awkward. Speeding up approvals could inflame environmental and local opposition, while allowing delays to mount risks leaving a flagship growth project stuck in limbo for another decade. Either way, the third runway now looks less like a mid-2020s decision and more like a long-term test of whether the UK can translate infrastructure pledges into delivery.