The Government has not made a sufficient case for a third runway at Heathrow and is relying too heavily on evidence dating back almost a decade, London Mayor Sir Sadiq Khan has warned.
Ministers are considering proposals for the expansion of the West London airport after backing a third runway earlier this year, despite longstanding opposition from environmental groups and some local communities.
Sir Sadiq, who has opposed Heathrow expansion for years, has raised fresh concerns over its potential impact on air pollution, noise, transport infrastructure and the UK’s climate commitments.
In a submission to the House of Commons Transport Committee, the Mayor and Transport for London (TfL) argue that the case for increasing Heathrow’s capacity “relies heavily” on findings from the Airports Commission dating back to 2015.
They say there has since been a significant change in circumstances, including changing patterns of business travel, expansion at other UK airports and new Net Zero commitments.
The submission argues there is a “significant gap between the strategic narrative and the evidence presented”.
It adds: “Many of the benefits underpinning the government’s argument are uncertain, only partially quantified, outside the core appraisal framework, or require complementary policies beyond airport expansion which are not assessed.”
Pollution concerns
Environmental impact remains one of the Mayor’s main objections.
City Hall and TfL argue that revised environmental tests do not provide sufficient reassurance that Heathrow can expand without “very serious environmental impacts”.
They are particularly concerned that improvements in London’s wider air quality could effectively create room for additional pollution generated by an expanded airport.
Policies including the Ultra Low Emission Zone (ULEZ) have contributed to reductions in pollution across the capital. Around Heathrow, average nitrogen dioxide concentrations have fallen by 34 per cent, while PM2.5 concentrations have dropped by 28 per cent, according to the submission.
“This progress must not be undone by the expansion,” it warns.
60,000 extra road journeys a day
Transport capacity is another major concern, with Heathrow’s annual passenger numbers projected to rise by 79 per cent to around 150 million following expansion.
The submission estimates this could generate an additional 60,000 highway trips every day – around 22 million a year – unless there is a major shift towards public transport.
It warns that additional traffic could place “intolerable strain on the highway network”, increasing congestion, pollution and carbon emissions.
Ministers have suggested Heathrow could expand without increasing the number of road journeys to and from the airport.
But achieving this would require the proportion of passengers travelling by public transport to rise from 39 per cent to 65 per cent.
TfL argues that would be difficult without additional rail capacity and connections.
While upgrades to the Piccadilly line and additional capacity on the Elizabeth line could help, the submission says direct services to destinations including Waterloo, Basingstoke and Reading would also be required.
Noise impact
The Mayor has also challenged proposals requiring an expanded Heathrow to produce no more noise than levels recorded in 2024.
He argues this could mean improvements from quieter aircraft and new technology are instead used to accommodate additional flights, rather than giving communities surrounding the airport the benefit of reduced noise.
The Government is aiming to secure planning approval for Heathrow expansion by 2029, with a third runway potentially operational by 2035.
A Department for Transport spokesperson has previously said: “Airport expansion will unlock jobs, strengthen Britain’s connectivity, and attract international investment, and we have been clear that it must support our decarbonisation goals while minimising impacts on local communities.”
