The UK and Welsh governments will be required by law to draw up new plans to cure illegal levels of air pollution, following a third defeat in the High Court in London to environmental activists ClientEarth.

ClientEarth has won three court cases against the UK government for poor air quality

It follows a hearing in January, during which the organisation told the court that plans to curb the UK’s illegal air pollution were inadequate – the judge, Mr Justice Garnham, had reserved judgment until this morning.

During the hearing, ClientEarth criticised the UK government’s air quality plans for not outlining measures to reduce pollution levels in 45 local authority areas, and said it had backtracked on Clean Air Zones in Birmingham, Leeds, Nottingham and Southampton – which it believes should be mandatory.

Ministers in 33 of the 45 local authorities will be required to identify pollution-curbing measures as soon as possible, the other 12 are projected to be legal by the end of 2018. However, there was no ruling regarding the five ‘Clean Air Zone’ cities as directions were issued from the government in December, requiring them to put a business case together to improve air quality.

The Welsh government admitted in January that not developing plans to improve air quality in Wales was illegal – today’s ruling means it will have to have a draft plan in pace by 30 April 2018, and a final plan in place by 31 July 2018.

The ruling is likely to accelerate the roll-out of clean air zones in cities across the country, and could also have a bearing on future taxation structures, both of which would affect fleets. It also enables ClientEarth to more quickly bring the UK government back into court, without applying for permission to bring a judicial view, if it deems future air quality plans to be unlawful. A move described as “exceptional” by Mr Justice Garnham.

“The history of this litigation shows that good faith, hard work and sincere promises are not enough, and it seems court must keep the pressure on to ensure compliance is actually achieved,” he said.

ClientEarth lawyer, Anna Heslop, commented: “The problem was supposed to be cleaned up over eight years ago, and yet successive governments have failed to do enough. The people who live in areas of the countries covered by this judgment deserve to be able breathe clean air and the government must now do all it can to make that happen quickly.”

The UK is one of nine EU Member States currently under threat of going through the European Court of Justice for not doing enough to tackle air pollution.