Heathrow expansion an 'outdated' risk, mayor says

An important development from the financial markets: Heathrow expansion an 'outdated' risk, mayor saysImage source, Getty ImagesImage caption, Proposals for a third runway have been hotly debated for more than two decadesByJames W KellyLondonPublished3 September 2026The London mayor has formally opposed plans for a third runway at Heathrow Airport, arguing the expansion threatens environmental targets and transport networks. City Hall and Transport for London (TfL) submitted a joint response to the government's draft Heathrow Expansion National Policy Statement (HENPS) consultation. Sir Sadiq Khan claimed the strategic case relied on outdated evidence that "fails to reflect current climate laws and travel habits".

The government said it was reviewing the response, while Heathrow questioned many of the claims made in City Hall's submission. The airport said the expansion was the "most important economic growth opportunity available to the UK". But Sir Sadiq said he saw no evidence the proposals were compatible with a credible path to net zero.

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"The evidence suggests Heathrow expansion is a risk that we simply cannot afford to take. "City Hall said additional flights could reverse the progress in reducing air pollution in communities surrounding Heathrow brought by the Ultra Low Emission Zone (Ulez). Image source, PA MediaImage caption, Sir Sadiq Khan said he will continue to "vehemently" oppose a third runwayThe submission raised several issues regarding infrastructure and finance:It estimates targets in the draft policy could generate 60,000 additional daily highway trips, adding 22 million road journeys annually to the M4 and M25Capacity upgrades would be needed for the Elizabeth and Piccadilly lines, alongside new southern and western rail links.

The submission puts the potential surface access cost at £9bn, noting no funding agreement existsA 58% increase in flights would reduce predictable noise respite periods for local residents from 50% to 25% of the day"The whole case for Heathrow expansion relies on outdated evidence that fails to take into account the urgent challenges we face today," Sir Sadiq said. "I will continue to vehemently oppose these plans as I seek to build a fairer, safer, greener, more prosperous London for everyone. "Heathrow Airport Limited is preparing plans for a new 2.

5km) northwest runway - which would require realigning a section of the M25 - with a final decision expected following a parliamentary vote in 2029. Image source, Getty ImagesImage caption, Heathrow Airport said expansion could unlock jobs and economic growth A spokesperson for the airport rejected claims that expansion was incompatible with net zero goals - and said the airport was committed to a completely privately-funded noise insulation scheme for local homes. On transport infrastructure, Heathrow stated its expansion plans include widening a busy stretch of the M25, adding that it will present "viable and funded solutions" for required public transport upgrades as part of the planning process.

Financial markets are tracking the development closely as investors assess the likely impact.