The UK faces fines of up to £300 million after receiving a warning from the European Commission over London's air quality.
The Commission delivered its second and "final" warning to the Government yesterday in response to dangerously high levels of airborne particles, known as PM10s, in London and Gibraltar.
The UK faces the threat of action in the European Court of Justice if it fails to meet EU limits on PM10s by 2011.
"Air pollution is bad for our health," said EU environment commissioner Janez Potocnik. "It reduces human life expectancy by more than eight months on average and by more than two years in the most polluted cities and regions."
According to the charity Environmental Protection UK, particle pollution kills 35,000 people in the country every year – up to 4,300 of them in London alone.
"It's disappointing that the commission has felt it necessary to issue a second and final written warning," a spokesperson for the Department for Environment, Food and Rural Affairs (Defra) told the BBC.
The Government received its first warning over London's air quality in 2009. Since then, the Commission said, it had seen no evidence that London had taken action to clean up its air, and was not on course to meet EU limits by the 2011 deadline.
London mayor Boris Johnson has launched an air quality strategy, aiming to ban taxis more than 10 years old by 2015. These are believed to be the biggest source of PM10 particles, as a result of emissions from exhausts as well as brake and tyre wear.
Johnson has been criticised over plans to scrap the western extension of London's congestion charge zone. He also suspended the third phase of a low-emission zone for vehicles in the capital, which would have seen the most polluting vans being charged £100 a day.
But while the air in the capital remains mucky, the water in the Thames is cleaner than it has been in years. And a new £270 million desalination plant that opened this week at Beckton will turn a mix of sea and river water into safe drinking water, Thames Water said.