Sadiq Khan: Heathrow expansion case relies on old data
Mayor of London's submission to Parliament criticises government evidence for third runway plan.
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The government's argument for expanding Heathrow Airport with a third runway is not sufficiently made and relies on outdated evidence from 2015, the Mayor of London has stated. Ministers are reviewing proposals for the expansion, which they backed earlier this year despite opposition from local and environmental groups.
Sir Sadiq Khan has opposed the expansion for years, citing concerns over noise, air pollution, and meeting climate change targets. In a submission to the House of Commons Transport Committee, the Mayor and Transport for London (TfL) argued that the government's case for increased capacity at Heathrow "relies heavily" on findings that are nearly a decade old.
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Criticism of government evidence
The Department for Transport published the Heathrow Expansion National Policy Statement (HENPS) in June, intended to form the basis for decision-making on any development consent application for a new runway. However, City Hall stated there is a "significant gap between the strategic narrative and the evidence presented." The submission noted that many benefits cited by the government are uncertain, only partially quantified, outside the core appraisal framework, or depend on complementary policies not yet assessed.
The submission accuses the government of inadequately accounting for material changes since the 2015 Airports Commission report, which recommended a new runway. These changes include a drop in business travel, the expansion of other UK airports, and new Net Zero carbon emission targets. The Mayor and TfL also claimed that revised environmental tests do not provide sufficient reassurance that an expanded Heathrow can be delivered without serious environmental impacts.
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The current approach, they suggested, would allow more flights and associated emissions by taking advantage of environmental improvements unrelated to the airport expansion itself. This, the Mayor said, would allow ministers to benefit from improvements made in London through policies like the Ultra Low Emission Zone (ULEZ), which has helped the city meet legal air pollution limits much earlier than predicted. In the Heathrow area, average NO2 concentrations have decreased by 34 per cent, and PM2.5 concentrations by 28 per cent. The submission warns that this progress must not be undone by the expansion.
Impact on noise and transport
The HENPS states that a third runway must not result in more noise than recorded in 2024. However, the Mayor argued this would prevent local communities from benefiting from reductions in noise due to technological and operational advances, as these benefits would instead be used to permit more flights. Annual passenger numbers at Heathrow are projected to increase by 79 per cent to 150 million if a third runway is built. This could lead to an estimated 60,000 additional highway trips daily, creating "intolerable strain on the highway network" and worsening congestion, air pollution, and carbon emissions.
Both TfL and the Greater London Authority (GLA) welcome the recognition of the need for a significant shift towards more sustainable transport modes. Ministers suggest Heathrow can expand without increasing road trips if the proportion of passengers using public transport rises from 39 to 65 per cent. TfL's analysis indicates this is unachievable without increased rail connectivity and capacity. While the Piccadilly Line upgrade and new Elizabeth Line trains would add capacity, direct services to destinations like Waterloo, Basingstoke, and Reading would be necessary to meet the projected demand.
Next steps for expansion
There is no indication that the government plans to reverse its support for the third runway. Ministers aim for planning approval by 2029, with operations expected to begin by 2035. A Department for Transport spokesperson previously stated that airport expansion will "unlock jobs, strengthen Britain’s connectivity, and attract international investment," and must support decarbonisation goals while minimising local impacts.
Questions this report answers
+What is the main criticism of the Heathrow expansion plan?
The Mayor of London argues the government's case for a third Heathrow runway relies on outdated 2015 evidence. City Hall's submission to Parliament states there is a significant gap between the government's narrative and the supporting evidence, and that environmental tests do not guarantee reduced impacts from expansion.
+What evidence does the Mayor cite for his concerns?
Sir Sadiq Khan points to the government's reliance on a 2015 Airports Commission report without adequately considering changes like reduced business travel and new Net Zero targets. He also highlights that while local air quality has improved, expansion could undo this progress.
+What are the projected impacts of a third runway?
Annual passenger numbers at Heathrow are forecast to rise by 79 per cent to 150 million. This could lead to 60,000 extra daily highway trips, increasing congestion and pollution. To mitigate this, public transport use would need to rise from 39 to 65 per cent.
+When could the third runway become operational?
The Department for Transport aims for planning approval for the third runway by 2029. Operations are projected to begin by 2035. The government states that the expansion must support decarbonisation goals and minimise impacts on local communities.
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