The failure to tackle excessive levels of air pollution in Glasgow and other cities has left the UK facing a legal threat from the European Commission (EC).

Limits on nitrogen dioxide, a toxic gas which mostly comes from traffic fumes, should have been met by January 2010 but the EC said that Westminster had failed to put plans in place to cut emissions.

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 Scotland's biggest city.

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

Friends of the Earth Scotland has warned that the health of thousands of Scots is being put at risk every year because of the failure to meet targets.

Their list of the most polluted streets in the country found fumes from exhausts breached air pollution safety limits at 26 urban sites across Scotland last year, with the worst levels recorded at Hope Street in Glasgow city centre.

Pollution hotspots were also found in Edinburgh, Aberdeen, Dundee, Paisley, Perth, Falkirk and several other towns. Bearsden was also highlighted.

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 include Greater London, the West Midlands, Greater Manchester, West Yorkshire, Teesside, the Potteries, Hull, Southampton the East, the South East, the East Midlands, Merseyside, Yorkshire & Humberside, the West Midlands and north-east England.

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.

The launch of legal proceedings by the European Commission was welcomed by campaigners, who called for tough action to tackle air pollution in the UK.

James Thornton, chief executive of environmental lawyers ClientEarth who brought the case to the Supreme Court, said: "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."

A spokesman for the Department for Environment, Food and Rural Affairs (Defra) said: "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.