LONDON London and two other densely populated areas in Britain will not meet European Union pollution limits until after 2030, 20 years after the original deadline, the bloc's top court heard on Thursday.
Under the EU's Air Quality Directive, member states were supposed to comply with limits on nitrogen dioxide (NO2) in 2010, but could extend that to 2015 if they delivered plans to deal with high levels of the colorless, odorless gas.
NO2 is mainly produced by diesel engines and is harmful to respiratory systems.
A scientific study in the European Respiratory Journal this year said NO2 could have the same effects on mortality as another pollutant, particulate matter 2.5, which government advisers have said causes 29,000 premature deaths in Britain each year.
Data from Britain's Department for Environment, Food and Rural Affairs (Defra) showed late on Wednesday that only five out of the country's 43 pollution zones will comply with EU limits on NO2 levels by 2015, and three zones - Greater London, the West Midlands and West Yorkshire - will not comply until after 2030.
Defra had previously said London would comply by 2025.
Lawyers representing the European Commission told the European Court of Justice (ECJ) on Thursday that the case was "a matter of life and death" and "perhaps the longest-running infringement of EU law in history."
The ECJ will make a final ruling by the end of the year on what action Britain needs to take, which will also be binding for all EU national courts. The case will then go back to the UK Supreme Court next year for its final judgment.
"Another five years of delay means thousands more people will die or be made seriously ill. The UK needs to act now to get deadly diesel vehicles out of our towns and cities," said Alan Andrews at environmental law firm ClientEarth, which brought the case against the government.
A spokeswoman for Defra told Reuters the government is reviewing its efforts to ensure Britain can comply with NO2 limits in the shortest possible time.
In February, the European Commission put more pressure on Britain by launching a separate but almost identical case to ClientEarth's for NO2 breaches.
The ECJ is not expected to rule on this until 2016 and could eventually issue fines which reach hundreds of millions of euros. However, it is more likely that the ClientEarth case will force Britain to take action to lower NO2 emissions.
Britain has a particular problem with NO2, but the Commission is taking action against 17 other member states - including France, Germany and Sweden - for breaching limits for particulate matter, another harmful pollutant.
As the ECJ's judgment in the ClientEarth case will come first, the Commission could use this to accelerate its cases against other member states.
"This case against Britain is the guinea pig. It begs the question of who will be next?" Andrews said.
(Editing by Susan Fenton)