Heathrow third runway opposed by Sadiq Khan over £9bn transport gap

The Mayor of London, Sadiq Khan, has formally opposed plans for a third runway at Heathrow Airport, warning the expansion would undermine climate targets and overwhelm London’s transport network. In a joint submission with Transport for London (TfL) to the government’s draft Heathrow Expansion National Policy Statement, Khan argued the proposals rely on outdated evidence that fails to account for current climate laws and travel habits.

TfL estimates the expansion could generate 60,000 additional daily highway trips, equivalent to 22 million extra car journeys annually on the M4 and M25. The authority also projects a 58% increase in flights would reduce predictable noise respite periods for local residents from 50% to 25% of the day. Upgrades to the Elizabeth and Piccadilly lines, alongside new southern and western rail links, are required, with TfL putting the potential surface access cost at £9 billion. No funding agreement for these upgrades has been secured.

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Climate and pollution concerns

Khan said there was no evidence the expansion was compatible with a credible path to net zero. City Hall warned additional flights could reverse progress in reducing air pollution in communities near Heathrow, particularly gains made through the Ultra Low Emission Zone (Ulez). The mayor stated, "The evidence suggests Heathrow expansion is a risk that we simply cannot afford to take."

The whole case for Heathrow expansion relies on outdated evidence that fails to take into account the urgent challenges we face today.

Sadiq Khan, Mayor of London

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Heathrow Airport Limited disputed the claims, stating the expansion was the "most important economic growth opportunity available to the UK." A spokesperson said the project would unlock growth, create over 100,000 jobs, and boost British trade by £150 billion. The airport also committed to a privately funded noise insulation scheme for local homes and pledged to present "viable and funded solutions" for public transport upgrades during the planning process.

Political and local divisions

Khan’s opposition is backed by a coalition of London and home counties council leaders, including Wandsworth, Richmond, Kingston, Hillingdon, Southwark, Sutton, and Windsor and Maidenhead. In a joint letter to Transport Secretary Heidi Alexander, the cross-party group urged the government to withdraw support for the third runway.

The Back Heathrow campaign, which supports expansion, countered that the councils’ stance was "not representative" of local residents. Executive director Parmjit Dhanda said more than 100,000 local members back the project, citing potential jobs, trade, and economic growth. Dhanda described a new runway as "way overdue."

Next steps

The Department for Transport, which has supported expansion under Keir Starmer’s government, said it would "carefully consider all responses" before setting out next steps later this year. A spokesperson emphasised that expansion would only proceed if it met legally binding climate obligations and strict environmental rules on air quality and noise pollution.

Heathrow’s plans include a 2.1-mile northwest runway, requiring realignment of a section of the M25. A final decision on the project is expected following a parliamentary vote in 2029.