London's air pollution levels, monitoring and EU limits
18 March 2012 Last updated at 15:32 GMT
The Department of Environment has claimed London's air pollution levels are getting better and EU targets for 2011 were met.
Andrew Cryan reports on claims that some of the worst readings in the capital were not being passing on.
One site being monitored by Brent Council is said to have failed standards 22 times so far this year, and would lead to illegal readings under EU levels.