Heathrow expansion an 'outdated' risk, mayor says

London's mayor has formally opposed plans for a third runway at Heathrow Airport, calling the expansion an "outdated" risk that jeopardizes environmental targets and transport networks. Proposals for the runway have been debated for over two decades.

City Hall and Transport for London (TfL) jointly submitted their response to the government's draft Heathrow Expansion National Policy Statement (HENPS) consultation. Mayor Sadiq Khan asserted that the strategic case relies on outdated evidence that "fails to reflect current climate laws and travel habits."

While the government stated it is reviewing the response, Heathrow Airport challenged many of the claims made in City Hall's submission, arguing that the expansion represents the "most important economic growth opportunity available to the UK."

However, Sir Sadiq stated he saw no evidence that the proposals align with a credible path to net zero, adding, "The evidence suggests Heathrow expansion is a risk that we simply cannot afford to take." City Hall warned that additional flights could reverse progress in reducing air pollution in communities surrounding Heathrow, achieved by the Ultra Low Emission Zone (Ulez). Sir Sadiq Khan reiterated his commitment to "vehemently" oppose a third runway.

The submission highlighted several infrastructure and financial concerns:

* TfL estimates that targets in the draft policy could generate 60,000 additional daily highway trips, leading to an extra 22 million road journeys annually on the M4 and M25.

* Capacity upgrades would be necessary for the Elizabeth and Piccadilly lines, along with new southern and western rail links. TfL estimated the potential surface access cost at £9bn, noting the absence of a funding agreement.

* TfL also stated that a 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"The whole case for Heathrow expansion relies on outdated evidence that fails to take into account the urgent challenges we face today," Sir Sadiq said.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 developing plans for a new 2.1-mile (3.5km) northwest runway, which would necessitate realigning a section of the M25. A final decision is anticipated following a parliamentary vote in 2029.

A spokesperson for Heathrow Airport rejected claims that expansion is incompatible with net zero goals, affirming the airport's commitment to a completely privately-funded noise insulation scheme for local homes. Regarding transport infrastructure, Heathrow stated its expansion plans include widening a busy stretch of the M25 and that it will present "viable and funded solutions" for required public transport upgrades as part of the planning process.

"This is about much more than a new runway," the spokesperson said. "It's about unlocking growth and over 100,000 jobs for the whole country, boosting British trade by £150bn, making travel more affordable and revitalising the UK's steel industry."

The mayor's position is supported 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 after the consultation closed, the cross-party group urged the government to withdraw support for the third runway.

However, the Back Heathrow campaign countered the councils, claiming their opposition was "not representative" of local residents. Executive director Parmjit Dhanda stated that over 100,000 local members support the expansion, citing the potential for jobs, trade, and economic growth, adding that a new runway was "way overdue."

The Department for Transport, which backed expansion under Keir Starmer's premiership in 2025, said ministers would "carefully consider all responses before setting out next steps later this year." A spokesperson for the department added, "We have always been clear that expansion will only go ahead if it is delivered in line with our legally binding climate change obligations, and meets strict environmental rules on air quality and noise pollution."

**Analysis by Tom Edwards, BBC London transport correspondent:**

The mayor and TfL's opposition to Heathrow expansion remains consistent, with ongoing concerns about noise pollution, public transport, and increased traffic. What has changed is their belief that the modeling is outdated, and their language appears to have become more forceful. Perhaps Ulez has emboldened the mayor to be more direct. TfL noted that since the pandemic, the world has changed with a decline in business travel, and they argue that the figures used to support expansion are over ten years old and no longer relevant. This sets the mayor on a potential collision course with the pro-expansion lobby, including some within his own party.