Deaths linked to air pollution fell by an estimated 40% in London over the five years from 2019, according to new analysis.

The city’s mayor, Sadiq Khan, welcomed what he called “overwhelming evidence” that his ultra-low emission zone was saving lives.

The figures come from a study by Imperial College London which also found that toxic air pollution in London had reduced sharply, with nitrogen dioxide levels down 41% and fine particulate pollution down 28%.

Imperial’s researchers said updated scientific evidence showed that the impact of air pollution on health was greater than previously understood, with previous estimates attributing 4,000 premature deaths in 2019 to air pollution.

That figure has been revised up to an estimated 6,400-8,000 premature deaths in 2019, falling to 3,800-5,100 in 2024.

Dr David Dajnak, from the Imperial Environmental Research Group, said: “Our study highlights two key findings: London’s air quality has improved markedly since 2019, but despite this progress, air pollution remains a serious public health risk.”

Recent evidence shows stronger associations between air pollution and cardiovascular conditions, dementia and diabetes, as well as respiratory diseases.

The research found that the boroughs with the highest ratio of deaths attributable to air pollution in 2024 were in outer London, including Bexley, Havering and Sutton, which City Hall said underlined the significance of Khan’s decision to push through the expansion of the Ulez to the whole of the capital, in the face of widespread local opposition, in 2023.

While the independent Imperial report itself does not single out the Ulez or any other policy, Khan said: “The evidence is now overwhelming and unarguable: the bold action we have taken in London has reduced pollution, improved public health and saved lives.

“This latest data shows why expanding Ulez London-wide was even more important than we previously thought and is transforming lives right across our capital.”

The Ulez was launched in 2019 in central London and widened across inner boroughs in 2021.

Vehicles that fail to comply with emission standards – typically those with diesel engines from before 2015 or petrol from before 2004 – have to pay a daily charge, starting from £12.50 for cars. The overwhelming majority of vehicles driving in the zone, about 97%, are now compliant.

A study last year for the Greater London Authority showed that roadside NO₂ pollution was 27% lower than expected had the Ulez not been introduced.

Khan is due to visit a primary school in east London on Wednesday, echoing a visit he made when first elected in 2016 when he pledged to speed through policies to clean up London’s air. Other measures beyond Ulez included providing £2.7m for indoor air quality filters for classrooms in 200 primary schools, and increasing the number of zero emission buses in Transport for London’s fleet from 30 to more than 3,000 in the last decade.

Prof Stephen Holgate, special adviser on air quality at the Royal College of Physicians said the scale of improvement shown in the study was “so encouraging” and “a powerful reminder that decisive, sustained action can deliver real, measurable benefits for people’s health”.

Jemima Hartshorn, of Mums for Lungs, said the research showed that Ulez did help clean up the air, but added: “Over 100,000 children went to hospital with breathing issues in London in 2024. And other cities and regions are still more polluted. Londoners need more action, and so does the rest of the country.”