LONDON British judges ruled on Wednesday that the government has breached European Union air quality law and asked the European Court of Justice (ECJ) for guidance on what action needs to be taken, delaying immediate improvements to air pollution.
Britain's highest appeal court, the Supreme Court, said the government was in breach of an EU directive which put limits on nitrogen dioxide (NO2) - a colourless, odourless gas produced by burning fuels which can damage people's breathing.
London has the highest levels of NO2 of any European capital. Around 29,000 early deaths a year in Britain are attributed to air pollution, according to a body which advises the government.
Before deciding on further action, the Supreme Court referred a number of legal questions to the ECJ in Luxembourg, which could take up to 18 months to answer.
The Supreme Court could eventually force the government to take certain steps to improve air quality but does not have the power to issue fines, according to Alan Andrews, lawyer at the firm ClientEarth which brought the case against the government in 2011.
The environmental law firm wanted to force the government to come up with an air quality plan to comply with European Union limits on N02 concentrations by 2015.
The High Court and the Court of Appeal refused to take action on the issue and the case went to the Supreme Court.
Under the EU directive, member states were supposed to comply with limits on NO2 in 2010 but the deadline could be extended by five years if a plan to deal with high levels of NO2 was delivered.
Court documents show 40 out of Britain's 43 air quality zones exceeded the limits for 2010 and the government's Department for Environment, Food and Rural Affairs (Defra) has said 23 zones might comply by 2015 and 16 between 2015 and 2020, while London is not expected to comply before 2025.
"This historic ruling marks a turning point in the fight for clean air and will pile the pressure on Owen Paterson," said James Thornton, chief executive of ClientEarth, referring to the UK Secretary of State for Environment, Food and Rural Affairs.
"He must now come up with an ambitious plan to protect people from carcinogenic diesel fumes," he added, which are largely blamed for creating NO2.
A spokesman for the European Commission said the body could already take legal action against Britain.
"It has not been done yet because we're working through a number of countries because it's easier to bring one horizontal action (against them all)," said spokesman Joe Hennon.
(Editing by Keiron Henderson)