The High Court is to rule on whether Government plans to tackle air pollution are “unlawful”.
Environmental lawyers from ClientEarth launched a third legal challenge last month against proposals for reducing illegal levels of harmful nitrogen dioxide.
Mr Justice Garnham will deliver his ruling on the case in London on Wednesday.
The charity’s legal team previously told the court that, eight years after the UK was found to be in breach of European Union limits on the pollutant, levels were still too high in 37 out of 43 zones across the country.
Nathalie Lieven QC said: “On Defra’s (Department for Environment, Food and Rural Affairs) own assessment, there continues to be a very significant impact on human health for many years into the future.”
The charity won two previous rulings against ministers over failures to meet legal limits for the pollutant.
Its latest case was brought against the Environment Secretary and the Transport Secretary, while a claim against the Welsh Government was discontinued after it agreed to work with ClientEarth on new proposals.
The charity wants a declaration that current plans to improve air quality are “unlawful” because they do not bring nitrogen dioxide levels within legal limits in the “shortest possible time”.
ClientEarth also asked for an order forcing the Government to propose and implement extra measures urgently, to “rectify shortcomings” within the present scheme.
During a hearing in January, Ms Lieven said levels will not be within legal limits until 2028 in London and 2021 in the majority of other zones around the UK unless further action is taken.
She argued the Government should consider additional measures in five cities where clean air zones will be introduced by next year and said there were “no concrete plans” for reducing nitrogen dioxide levels in 45 local authorities.
Lawyers representing the Government urged Mr Justice Garnham to dismiss the charity’s case.
Kassie Smith QC, for the Environment Secretary, argued the complaints made about the Government’s plans were “misconceived”, as work was being undertaken to improve air quality in each of the five cities and 45 local authority areas.
She also said new measures could not be introduced in time to “bring forward” the Government’s compliance with the legal limits.
The Government’s measures to tackle air pollution include stopping the sale of diesel cars (Yuki Mok/PA)
Following previous court orders, ministers revealed plans for reducing nitrogen dioxide, much of which comes from vehicles, to within legal limits in July.
The measures included £255 million to help local authorities come up with ways to improve air quality, and proposals to end the sale of all conventional petrol and diesel cars by 2040.
A Defra spokeswoman said: “Air pollution has improved significantly since 2010, but we recognise there is more to do which is why we have put in place a £3.5 billion plan to improve air quality and reduce harmful emissions.
“We will also end the sale of conventional new diesel and petrol cars and vans by 2040, and this year we will publish a comprehensive clean air strategy which will set out further steps to tackle air pollution.”