Heathrow’s proposed third runway is facing renewed political uncertainty after Prime Minister Andy Burnham stopped short of backing the project and questioned whether spare capacity at other UK airports should be used before Heathrow expands.
The shift comes as Heathrow has acknowledged that the government’s previous ambition to have a third runway operating by 2035 is unlikely to be achieved. The airport is still working towards securing planning permission in 2029, but says the runway would then take up to a decade to become operational.
That points instead to an opening around 2039.
The combination leaves Heathrow in a different political position from a year ago, when the government explicitly backed expansion, selected Heathrow Airport Limited’s north-west runway proposal to take forward and began reshaping national planning policy around it.
Burnham has not withdrawn that support.
But nor has he given the third runway the unequivocal backing it received under Keir Starmer.
Questioned about the project during Labour Party conference, Burnham said he was reluctant to state a firm position because Heathrow expansion remained subject to consultation and a possible future planning application.
He said there were strong views on both sides and that the issues needed to be considered independently and fairly.
Two days later, he went further. Burnham said there was a “strong case” for Heathrow expansion but raised the possibility that existing capacity elsewhere could be used first.
He pointed to Manchester Airport, where he said the second runway still had spare capacity, and argued that the country needed a wider discussion about the right balance of airport capacity.
That does not make Burnham an opponent of Heathrow expansion. But it introduces a question that was largely absent from government policy under Starmer: whether another runway at Heathrow is necessarily the preferred way to add aviation capacity.
The distinction matters because the project has already acquired substantial policy momentum.
The previous government selected Heathrow Airport Limited’s north-west runway proposal in November 2025 as the scheme on which its review of aviation planning policy would be based.
It subsequently published a draft Heathrow Expansion National Policy Statement in June 2026.
The document would establish the national planning framework against which a future application for Heathrow expansion would be assessed. It says any expansion must pass four tests covering economic growth, climate change, air quality and noise.
The government consultation on that policy closed on 1 September. Parliamentary scrutiny continues until 26 November.
But the National Policy Statement is not planning permission.
Heathrow remains in the pre-application stage of the Development Consent Order process. It will begin its own eight-week consultation on the detailed expansion scheme on 27 October, running until 22 December.
After that, Heathrow would still have to submit a Development Consent Order application. The Planning Inspectorate would examine the scheme before a final decision by the Secretary of State.
The three stages therefore perform different roles. The government is deciding the national policy framework, Heathrow is consulting on its actual scheme and any eventual planning application would be considered separately.
That makes Burnham’s caution understandable in procedural terms, but it also creates uncertainty over how strongly the government will continue to champion the project while those processes run.
Heathrow argues that expansion is needed because the airport is operating at capacity.
Its £33bn expansion plan would add a third runway and further terminal capacity. Heathrow says this could increase capacity by about 50 per cent, allowing up to 756,000 flights and 150mn passengers a year.
Part of the M25 would also have to be rerouted, including construction of a tunnel beneath the new runway.
Heathrow argues that the additional capacity would increase competition between airlines, add international routes and strengthen the UK’s trade and investment links.
The government’s own economic modelling provides some support for the growth case, although it also puts its scale into context.
The Department for Transport’s core scenario estimates that expansion would increase annual UK GDP by about £2.6bn in 2056 compared with a scenario without expansion. That represents an increase of about 0.05 per cent.
Its modelling also estimates expansion could support between 50,000 and 61,000 additional local jobs by 2055, including direct, indirect and induced employment.
Those benefits have to be weighed against a project that would require more than £30bn of private investment and substantial associated infrastructure, while increasing aviation capacity in a country with legally binding climate targets.
Noise, air quality, surface transport, disruption to surrounding communities and the financing of the development remain important parts of the planning argument.
The government’s four tests are intended to determine whether Heathrow can meet those requirements while providing sufficient economic benefit.
The political test is becoming less clear.
Under Starmer, government support for the third runway was presented as part of a wider drive to increase investment and economic growth. Ministers wanted planning permission secured by 2029 and initially set an ambition for the runway to operate by 2035.
Heathrow still aims to secure consent by 2029, but its current timetable implies the runway could instead open around 2039.
Burnham has meanwhile inherited a policy process designed to enable the project while making clear that he wants to hear the arguments against it and consider how Heathrow fits into a wider national aviation strategy.
That leaves the third runway neither abandoned nor politically secure.
Heathrow now has to progress its scheme through a planning process while the government decides whether the policy commitment it inherited should continue in its existing form.
The next test comes quickly. Heathrow opens its own consultation on 27 October, followed by the end of parliamentary scrutiny of the government’s proposed planning framework on 26 November.