Heathrow Airport warned that its planned third runway may miss the government’s 2035 target, potentially delaying the new strip until 2039.

A missed deadline threatens travel plans

The airport, which handled 80 million passengers last year, is the UK’s busiest gateway to the world. A delay of four years would mean airlines and passengers face a prolonged period of congestion and higher operating costs.

Why the delay is unfolding

Heathrow said it now expects planning approval by 2029, after a series of legal challenges and a fresh environmental assessment. The government, which set 2035 as an ambitious target, has repeatedly said the deadline was never guaranteed.

The deadline has always been ambitious,
said a government minister, echoing comments from the airport’s chief executive.

Heathrow’s chief executive, David Ross, said the new timetable still offers a chance to meet the 2039 launch target, but he warned that the extra time would cost airlines and passengers more than the initial plan. The airport’s business case, which hinges on increased capacity, now faces a tighter window for securing funding and construction contracts.

Heathrow Airport runway under construction

Implications for the UK economy

Analysts estimate that the third runway could boost the UK economy by up to £20 billion a year, but a delay pushes those benefits further into the future. A 2025 study by the Airports Council International projected that airlines would need to add 1.5 million extra seats per year to meet demand by 2035, a figure that may be harder to achieve without the new runway.

Context and the road ahead

The project has faced opposition from environmental groups and local residents for years, with legal challenges in the High Court and the Supreme Court. Earlier this year, the government announced it would seek a new environmental assessment to address fresh concerns about wildlife and carbon emissions.

Heathrow now plans to submit a revised planning application in 2028, with construction slated to start the following year. The airport will need to secure investment from private partners and the government before the 2039 launch can be guaranteed.

Ministers will discuss the revised timetable at the upcoming infrastructure briefing on Thursday, with the deadline for planning permission set for 2029.