The plan from London’s political leaders, which prompted protests and sabotage, extends the Ultra Low Emission Zone (Ulez) to cover all the capital’s roads and extends it into surrounding counties.
Four Conservative-led outer London councils and Surrey County Council have challenged London Mayor Sadiq Khan's plan and now the High Court will hear the case just weeks before the Ulez expansion is set to take effect.
The new Ulez borders envisioned by London Mayor Sadiq Khan will reach Buckinghamshire, Essex, Hertfordshire, Kent and Surrey.
If it goes ahead, Ulez will see drivers in outer London pay a £12.50 ($16) daily fee from August 29 if their vehicles do not meet the required emissions standards.
The scheme was introduced in 2019 and is separate from the city's two-decades-old congestion charge for central London.
“They're hitting working-class people again,” said self-employed builder Chris Fordham, 62, who drives a non-compliant 2012 diesel van. “I'm thinking about packing up work.”
Environmental group Greenpeace criticised the councils for going to court, accusing them of “fighting completely the wrong battle”.
“They should be putting their energy and resources into bringing down air pollution, not a key anti-pollution measure,” said Areeba Hamid of Greenpeace UK.
The current Ulez is in force inside the North and South Circular roads – a perimeter route within the capital – and the expansion will take in all London boroughs.
Mr Khan insists the bigger Ulez will help improve the city's “toxic air pollution”, which causes thousands of annual deaths and life-changing illnesses.
An estimated 4,000 Londoners die prematurely each year from conditions related to air pollution, Mr Khan said.
He developed adult-onset asthma nine years ago and blames it on decades of breathing the capital's poor air.
In a legal first in 2021, a coroner ruled that poor air quality from vehicle emissions made a “material contribution” to the death of a nine-year-old London girl who suffered a severe asthma attack.
London's Ulez mirrors similar low-emission zones to improve air quality in more than 200 cities in 10 countries across Europe.
Mr Khan lacks the legal power to order the vast Ulez expansion, a lawyer for the councils told the High Court on Tuesday.
Craig Howell Williams said the mayor and Transport for London's (TfL) approach would bypass legal safeguards, which were "designed to ensure that any new charging scheme is properly considered before coming into effect".
Ben Jaffey KC, representing the mayor and TfL, said in written arguments the "primary objective" of the Ulez expansion was "to improve London's air quality, in particular reducing nitrogen oxides (NOx) and particulates".
He said the mayor had used his powers to change emissions zone rules in London many times in the past 16 years.
Petrol cars registered pre-2006 and diesel vehicles first registered before September 2015 are unlikely to meet the minimum emissions standards required.
TfL – a local government body that overseas the city's transport infrastructure – estimates that fewer than 200,000 such vehicles currently enter the new zone, based on existing Ulez camera analysis.
The RAC motoring group used a freedom of information request to discover that more than 850,000 ineligible vehicles are registered within London alone.
TfL also confirmed that more than 200 enforcement cameras have suffered sabotage.
TfL says all revenue is reinvested into running and improving the capital’s transport network, such as expanding bus routes in outer London.
The hearing, before Mr Justice Swift, is due to conclude on Wednesday, with the judge expected to give his verdict at a later date.