The Mayor of London has hailed his controversial Ultra Low Emission Zone (ULEZ) policy as “bold” and “transformative” two years after its expansion to the outer boroughs – but has it been a success?
ULEZ, first introduced in 2019, has been expanded twice – once in 2021 to cover anything inside the North and South Circular roads, and again on August 29, 2023 to cover all 32 London boroughs.
Today marks the two-year anniversary of the full rollout, which sparked anger, legal challenge and a lot of debate on social media – but the silent majority appear to have spoken when Sir Sadiq won a landmark third term at this year’s Mayoral election despite the belief ULEZ might be his downfall.
The Local Democracy Reporting Service (LDRS) has taken a look at what’s happened since the expansion, and whether it can be considered a success.
What was the point of ULEZ and has it delivered?
The London-wide zone measures 1,500 km2 and covers nine million people, making it the largest of its kind in the world.
The intention is simple – to improve London’s air quality by discouraging the most polluting vehicles from being on the roads.
To do this, drivers of older cars which fail to meet emission standards are compelled to pay a £12.50 fee for every day they drive in any of London’s boroughs. This applies largely to pre-2005 petrol vehicles and pre-2015 diesel models.
Both the introduction and expansion of ULEZ were seen as an unfair tax on motorists by critics.
Two years on, however, it’s clear that the clean air zone has played some part in clearing up London’s traditional smog.
Figures from the Mayor’s Office have revealed that NOx emissions, which can cause inflammation of the airways and increase susceptibility to respiratory infections and to allergens, were estimated to be 36 per cent lower in 2024 than they would have been had ULEZ not been introduced.
This figure was 14 per cent in Outer London. The region also saw an 82 per cent reduction in people exposed to illegal levels of pollution.
Similarly, concentrations of NO2, or nitrogen dioxide, were estimated to be 54 per cent lower in Central London, and 27 per cent lower across the whole of the capital.
Cumulatively, carbon emissions are estimated to be 813,000 tonnes lower due to ULEZ – the equivalent of nearly 3 million passenger trips between Heathrow and New York.
NOx (Nitrogen Oxide Emissions) – 36% lower in 2024 than without ULEZ
Roadside NO2 (Nitrogen Dioxide) Emissions – 27% lower across London, 54% lower in Central London, 29% lower in Inner London, and 24% lower in Outer London
Carbon Emissions – 813,000 tonnes lower compared to a ‘No ULEZ’ scenario
Illegal Pollution – 80% reduction in people exposed across London, including 82% in Outer London
Scrappage scheme – 53,058 vehicles removed from London’s roads
Vehicle Compliance – 97% of vehicles seen driving in March 2025 were ULEZ compliant
The Mayor of London said: “The ULEZ is the world’s largest clean air zone, and thanks to this bold policy and our other transformative air quality policies, all Londoners and visitors are now breathing cleaner air while thousands of polluting cars have been taken off our roads meaning levels of toxic air pollution have substantially decreased.
“Two years since ULEZ expanded London-wide, I’m proud the evidence shows it’s been even more effective than expected in helping to improve the health of Londoners, support children’s lung growth and ultimately save lives.
“Due to these pioneering policies, we are close to bringing air pollution within legal limits and I remain committed to improving air quality across the capital as we continue building a greener, fairer, better London for everyone.”
The introduction of the scheme was criticised for leaving some poorer Londoners facing a £12.50 daily charge if they could not afford a newer vehicle, or stopping using their car altogether.
However, the Scrappage scheme, which originally offered up to £7,000 compensation if a polluting car was handed over, paid out £186million for more than 53,000 older vehicles to help motorists. Of these units, 684 were donated to support medical and humanitarian efforts in Ukraine.
The results have prompted calls for the Mayor to go even further in his battle to clean up London’s air.
Caroline Russell, Green Party London Assembly Member and Leader of the Green Group, told the LDRS: “London’s air is 27% cleaner thanks to the ULEZ – proof that bold action works.
“The success of the ULEZ is testimony to the many campaigners who pushed and pushed for the Mayor to act, so that Londoners can trust the air they breathe. But the work is far from over. Congestion is still a huge issue and more needs to be done to give people the confidence to ditch their cars for good.”
Opposition, legal challenges and vandalism
It been far from plain sailing, however.
As well as his political opponents, the Mayor of London has faced resistance from councils in London – four of whom launched a High Court challenge to the August 2023 expansion – and even his Labour Party colleagues.
MPs Seema Malhotra, Jon Cruddas, Siobhain McDonagh and Abena Oppong-Asare all came out publicly against the Outer London expansion.
A month prior to the move, Labour lost a high-profile by-election in Uxbridge and South Ruislip, prompting leader Sir Keir Starmer to urge Sir Sadiq to “reflect” on its rollout.
ULEZ infrastructure itself has also fallen victim to organised vandalism. So-called ‘Blade Runners’ said they intended to destroy all cameras tasked with enforcing the scheme.
The Mayor of London has refused to budge on his support for ULEZ, saying in March that he has “no plans to move the goalposts” when it comes to vehicle standards. That same month, figures revealed that over 97 per cent of vehicles seen driving in London were ULEZ-compliant.
Yet he is still likely to face opposition from those wishing to reverse it. Last year the Conservative London Mayoral candidate Susan Hall pledged to scrap the Outer London expansion, largely pinning her election hopes to that pledge – this appeared to have backfired when Sir Sadiq won by a landslide.
It would be no surprise, however, if both the Tories and Reform UK ran on a similar policy next time around, in an attempt to tap into the anger that remains among some in the city’s outer boroughs.
Keith Prince, the City Hall Conservatives Transport Spokesman, told the LDRS: “Two years on, Sadiq Khan’s Outer London ULEZ has slapped drivers with over 2 million fines and £224 million from their pockets, yet pollution levels have barely shifted. This is nothing more than a cash grab to mask his wider failures at City Hall.”
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