While the UK isn't the world's worst offender when it comes to pollution *cough Delhi cough Beijing cough*, some of its cities are still failing to hit the EU's clean air standard targets. And that means a slap on the wrist in the courts.
The EU's air pollution directive was established in 2008, with the UK supposed to meet standards by 2010. This would have meant a significant reduction in nitrogen oxides and air borne contaminates such as particulate matter, which are dangerous to health and can lead to respiratory diseases. However, it's now unlikely the UK will meet standards before 2020 (rising to 2025 for London), with diesel engines the biggest offenders when it comes to pumping out pollutants.
The UK government has two months to respond to the European Commission, and could face a hefty fine from the European Court of Justice if it is found in breach of its role in the directive. With roughly half of all new car sales in the UK diesel powered, there may be little to argue. [BBC]