The Mayor of London, Sir Sadiq Khan, and Transport for London (TfL) have submitted a new critique to the House of Commons Transport Committee, arguing that the government's case for expanding Heathrow Airport is not "sufficiently made" and relies heavily on outdated evidence from 2015. The submission warns that the proposed third runway could lead to 22 million additional car journeys annually, undermining recent progress on air quality and climate targets.
Government's Case Based on Outdated Evidence
The Department for Transport published the Heathrow Expansion National Policy Statement (HENPS) in June to guide decisions on a development consent application for the new runway. However, City Hall claims there is a "significant gap between the strategic narrative and the evidence presented," noting that many benefits are "uncertain, only partially quantified, outside the core appraisal framework, or require complementary policies beyond airport expansion which are not assessed."
The written submission accuses the government of relying on the 2015 Airports Commission report, which recommended a new runway, without adequately accounting for material changes since then. These include a drop in business travel, the expansion of other UK airports, and new Net Zero carbon emissions targets.
Environmental Concerns and Air Quality Progress
The Mayor and TfL argue that revised environmental tests "do not provide sufficient reassurance that an expanded Heathrow can be delivered without very serious environmental impacts." They suggest the approach would allow more flights and emissions while "taking advantage of environmental improvements unrelated to airport expansion." Specifically, ministers could capitalise on "headroom" created by policies like the Ultra Low Emission Zone (ULEZ), which has helped London meet legal air pollution limits nearly 200 years earlier than predicted. In the Heathrow area, average NO2 concentrations have dropped by 34 per cent, and PM2.5 concentrations by 28 per cent. The submission warns: "This progress must not be undone by the expansion."
City Hall has highlighted these improvements, although the Mayor has admitted London will not achieve Net Zero status by 2030 as originally targeted.
Noise and Transport Impacts
The HENPS states that a third runway must not increase noise beyond 2024 levels. However, the Mayor contends this will "deny local communities the benefits of any reduction in noise that comes from technological and operational advances, as this will be used instead to enable more flights."
Annual passenger numbers at Heathrow are projected to rise by 79 per cent to 150 million if the runway is built. The submission predicts 60,000 extra highway trips daily, or 22 million annually, causing "intolerable strain on the highway network, worsening congestion, increasing air pollution and carbon emissions and eroding the economic benefits in the wider region."
TfL and the Greater London Authority (GLA) welcome recognition of the need for a shift to sustainable transport, but note that without a third runway, public transport use would need to rise from 39 to 65 per cent. TfL's analysis indicates this is impossible without additional rail capacity. While upgrades to the Piccadilly Line and new Elizabeth Line trains help, direct services to destinations like Waterloo, Basingstoke, and Reading would be needed.
Government's Stance and Next Steps
Ministers are aiming for planning approval by 2029 and operations by 2035. A Department for Transport spokesperson previously told the LDRS: "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." There is no indication the government will reverse its support for the third runway.
