In the EU, there are legal limits for a variety of pollutants. These limits are set out in the Ambient Air Quality Directive.
The UK is required to report on how it is performing against these legal limits. These reports give a good indication of where the problems are. If there is an illegal breach in one area of the UK, then the whole country is in breach. So if you look for your area in the government reports, remember that any law broken applies to the whole country.
Nitrogen dioxide (NO2), which primarily comes from diesel fumes, is a particular problem for the UK. There are dangerous, illegal levels of NO2 in many of our towns and cities. Very often we hear about the pollution levels in central London, but it is a problem nationwide.
ClientEarth are taking legal action against the UK Government for breaches of the NO2 limits. The European Commission has begun legal proceedings for the same reasons.