This is source I found from another site, main source you can find in last paragraph
The UK government is being sued for a third time over the widespread illegal levels of air pollution, which cause 40,000 early deaths every year.
Environmental lawyers ClientEarth have already defeated ministers twice in court, forcing a new pollution plan to be drawn up in July. But ClientEarth believes even the latest strategy does not meet the legal requirement of banishing toxic air in the “shortest possible time”, as EU law requires.
“The UK government’s stubborn failure to tackle illegal and harmful levels of pollution in this country means that we have no choice but to take legal action,” said James Thornton, ClientEarth’s CEO. “We need clarity from the government and for that we’ve been forced to go back to court.”
ClientEarth sent ministers a pre-action legal letter setting out their concerns in October but deemed the government’s response inadequate. They have now applied to the courts for a legal hearing. The government has already spent £370,000 of taxpayers’ money in failed attempts to fight air pollution court action.
Nitrogen dioxide pollution, mostly produced by diesel vehicles, has been illegally high in most urban parts of Britain since 2010. The government’s latest plan was condemned as “woefully inadequate” by city leaders and “inexcusable” by doctors.
Air pollution causes an estimated 23,500 early deaths every year from NO2, rising to 40,000 when other pollutants are considered. In September, the UN’s special rapporteur on pollution said the government was “flouting” its duty to protect the lives and health of its citizens and in October a major pollution report estimated the number of premature deaths in the UK at 50,000 per year.
Oliver Hayes, at Friends of the Earth, said: “It’s shameful that the government has to keep being taken to court to try to force it to protect the health of its citizens.”
ClientEarth believes there are several grounds for judicial review, including backtracking in the latest plan on “clear air zones” in Birmingham, Derby, Leeds, Nottingham and Southampton. These zones, which would use charges to deter polluting vehicles from city centres, were mandatory in previous plans but are now only “expected” to be implemented.
ClientEarth also say it is unacceptable that the plan requires no action in 45 local authorities with illegal levels of air pollution. These include Leicester, Oxford, Liverpool, Cheltenham and Sunderland, with the government arguing toxic air will fall to legal levels without enforced action.
However, Leicester and Oxford city councils have written to ministers saying that the government has seriously underestimated pollution levels and that by requiring no action, they are stopping the councils getting access to funding to cut pollution. Oxford is planning to ban all petrol and diesel vehicles in the future.
Source : https://www.theguardian.com/environment/2017/nov/07/uk-government-sued-for-third-time-over-deadly-air-pollution