London's airports

A greener future

Airports must play their part in tackling the climate emergency - reducing their carbon emissions will help London and the UK meet their net zero targets.

But almost every London airport is developing options to increase capacity and the Mayor is not convinced that these can be compatible with our climate change commitments.

He says airports must show that their plans will not cause significant environmental harm or put undue pressure on transport networks. Local communities and Londoners in general must not suffer increased noise or air pollution emissions or more traffic congestion as a result of an airport's plans.

Together with the Mayor we're actively engaging with and responding to consultations related to UK aviation in general, and airport expansion in particular. See these responses on the Aviation page in Publications & reports.

Heathrow expansion

The proposals for Heathrow expansion raise significant concerns about the impact on the environment and transport. After the Government announced in October 2016 that it would support a third runway at Heathrow Airport it prepared an Airports National Policy Statement (NPS) to enable it.

The Mayor has raised his concerns about Heathrow expansion at every stage of the process, including the consultations by Government on the NPS and by Heathrow Airport Limited (HAL) on its outline proposals.

Legal challenge

The Mayor, together with local authorities and environmental groups, then started a legal challenge against the NPS after it was designated by Government in June 2018.

The initial court ruling upheld the NPS. However, in February 2020 the Court of Appeal determined that the NPS was illegal on climate change grounds and suspended the NPS immediately.

This decision was challenged by HAL. In December 2020 the Supreme Court overturned the decision and reinstated the NPS.

HAL's preparations are currently on hold but it has indicated that it will restart planning for expansion in due course.

The Mayor remains very concerned about the impact of a third runway. He has resubmitted his request to Government for a formal review of the NPS and is committed to opposing expansion at Heathrow.

Impact of expansion

As part of our NPS response we did detailed analysis and modelling to understand how the expansion of Heathrow would affect road and rail access, air quality and noise. The serious issues raised as part of the NPS response have not been addressed by Heathrow in its DCO process.

Road and rail access

An expanded Heathrow Airport would mean an additional 170,000 trips by passengers and staff each day. The Government has suggested that Heathrow can expand without resulting in any extra road trips to and from the airport. For this to happen with a third runway, the percentage of people using public transport to get there would need to increase from 39% to 65%.

Our analysis indicates that this cannot happen without extra connectivity and capacity on the rail networks serving the airport. The Government's proposals do not currently guarantee the significant investment needed to create this, nor does Heathrow accept the need.

Air quality

Heathrow is one of the worst air pollution hotspots in London and legal limits for air quality are already exceeded in the surrounding area. Even without expansion bringing more flights and more journeys to and from the airport, there is a huge challenge to clean up the air.

Our analysis indicates that a bigger airport will make air pollution worse and neither the Government nor Heathrow have been able to show how legal limits for clean air can be met once a third runway is operating.


Unacceptable noise from the airport already affects far too many people - not just those in the immediate vicinity but also those who live under the flight paths across London and in neighbouring areas.

Our analysis indicates that at least 200,000 more people will be exposed to unacceptable levels of noise.


Neither Government nor Heathrow has shown how a third runway can operate without a material impact on the ability of the UK to stay within its carbon targets and budgets.