Rachel Reeves had reportedly been considering the expansion of the west London hub, as well as Gatwick and Luton airports, during a speech on growth next week.
But when asked in the Commons on Tuesday about the rumours, which were initially reported by Bloomberg, Ms Reeves replied: “I’m not going to comment on leaks”.
Plans to increase passenger capacity at the three London airports have prompted a furious reaction from environmental groups.
Jenny Bates, transport campaigner at Friends of the Earth, called the proposal for another runway at Heathrow “hugely irresponsible in the midst of a climate emergency”.
Alethea Warrington, from climate charity Possible, agreed: “Approving airport expansions would be a catastrophic misstep for a government which claims to be a climate leader.”
The prime minister’s spokesperson told Sky News: “The government is determined to get the economy growing, any airport expansion must demonstrate it contributes to economic growth and fits with environmental obligations.”
London mayor Sadiq Khan has been a fierce critic of attempts by Heathrow to build a third runway in west London, on the basis of the impact on air quality, noise and net-zero targets.
Despite construction receiving parliamentary approval in 2018, the plans have been delayed by legal challenges and the coronavirus pandemic.
A spokesperson for Heathrow would not comment on reporting about a third runway, but said “growing the economy means adding capacity at the UK’s hub airport which is full”.
In a statement to Sky News, the airport added it was “looking at potential options to deliver a third runway at Heathrow in line with strict tests on carbon, noise and air quality”.
Transport Secretary Heidi Alexander has a deadline of 27 February to make a decision on a second runway at Gatwick, which would effectively involve modifying an existing taxiway.
Gatwick’s majority owners, VINCI Airports, said the £2.2bn project would create 14,000 jobs and generate £1bn a year in economic benefits.
In a statement to Sky News, CEO Stewart Wingate said the airport in West Sussex could “be a major part of the government’s drive for growth”.
“We have put forward a strong and compelling case focused around making best use of our existing infrastructure, minimising noise and environmental impacts,” he said.
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But Communities Against Gatwick Noise and Emissions (CAGNE) insisted they would legally challenge any second runway.
Meanwhile, Luton Airport, owned by the local council in Bedfordshire, has applied to build a new terminal and asked for permission to increase its passenger numbers to 32 million a year. It carried about 16.7 million in 2024.
The airport’s CEO, Alberto Martin, suggested it would bring more jobs and long-term local benefits.
He described the expansion plans as fully aligning “with the government’s sustainable growth agenda by making best use of existing infrastructure”.
But Andrew Lambourne, from anti-noise campaign group LADACAN, described the prospect of expansion at Luton as “reckless folly”.
“We had hoped the Labour government understood what responsible economic sustainability means – but clearly not,” he told Sky News.
Dr Alex Chapman, senior economist at the New Economics Foundation (NEF), also suggested the suggested growth benefits of UK airport expansion don’t stack up.
He added: “The massive climate damage caused by these schemes will create deep physical and economic hardship for millions and will wipe out any benefit from the government’s other climate policy efforts almost overnight.”
