The European Commission launched legal action last month against the UK for its failure to cut excessive levels of air pollution.Limits on nitrogen dioxide, a toxic gas which mostly comes from traffic fumes, should have been met by January 2010.

Nitrogen dioxide leads to the formation of ground-level ozone, causing major respiratory problems and premature death, with city-dwellers particularly at risk in the face of high levels of traffic.

"This much-needed legal action will hopefully force the Government to take urgent steps to end a national scandal that causes tens of thousands of people to die prematurely each year because of air pollution. The Government, Mayor of London and local authorities must now take tough and rapid measures, such as reducing traffic levels, rather than increasing road-capacity. This would cut air pollution and congestion, and make our towns and cities cleaner, healthier places for people to live and work."

The UK Supreme Court has already declared that air pollution limits are regularly exceeded in 16 zones across the UK, the Commission said, including London, Manchester, swathes of England and Glasgow.

Extensions have been agreed with a number of European Union countries with "credible and workable" plans for improving air quality, to allow them until January 1, 2015 to meet the limits.

But the Commission said the UK had not presented any such plan for the areas in question, which are Greater London, the West Midlands, Greater Manchester, West Yorkshire, Teesside, the Potteries, Hull, Southampton, Glasgow, the East, the South East, the East Midlands, Merseyside, Yorkshire & Humberside, the West Midlands and the North East.

As a result the Commission said it was of the opinion the UK was in breach of its obligations under EU law on air pollution, and it had sent a letter of formal notice to the Government which has two months to respond.

If the UK fails to cut pollution it could face a legal process which could result in significant fines.

"We have the right to breathe clean air and the Government has a legal duty to protect us from air pollution. The Commission has singled out the UK following the Supreme Court's landmark decision last year. The UK has some of the highest levels of nitrogen dioxide in Europe."

"I hope this formal letter now sees a serious response and is the start of a process which will see London's air cleaned up, people's health improved - and a reduction in the number of Londoners dying prematurely each year due to air pollution: some 4,000 at last count. Poor air quality really is a matter of life and death, and I am shocked that the Government and the Mayor of London have repeatedly failed to take any significant action to improve it and meet their obligations. The latest figures show that some of the poorest areas of the capital have the worst air quality - so this isn't just a public health issue, it's an equality issue.Air pollution is largely caused by diesel exhaust fumes, and we need the Government, the Mayor of London and the London Borough councils to act to reduce them immediately."

"Air quality has improved significantly in recent decades. Just like for other Member States, meeting the NO2 limit values alongside busy roads has been a challenge. That is why we are investing heavily in transport measures to improve air quality around busy roads and we are working with the Commission to ensure this happens as soon as possible."

The Commission is currently taking action against 17 countries over air quality problems, but this is the first to address limits of nitrogen dioxide.