Campaigners have claimed the UK's air pollution problem could be worse than thought as a "citizen science" project showed dirty air across the country.
Thousands of people have taken part in the experiment run by Friends of the Earth to assess levels of pollutant nitrogen dioxide in local areas such as the street they live in or outside their children's schools over a period of two to four weeks.
The "clean air kits" give a snapshot of pollution and have recorded high nitrogen dioxide levels - which if they were seen across a year would breach legal limits - in 133 local authorities and in 181 parliamentary constituencies.
The number of areas recording high concentrations is greater than in Government documents, Friends of the Earth said.
The results also suggest there are 13 pollution hotspots across the country which are not currently identified as having a problem by their local authority or Government, the environmental group said.
Ministers must put in place measures to tackle air pollution in final air quality plans due to be published in July, they demanded.
These should include Government-funded and mandated clean air zones, with charges for the most polluting vehicles to enter areas with high air pollution, and for a diesel scrappage scheme.
Oliver Hayes, Friends of the Earth air pollution campaigner, said: "It's shocking that these early results suggest the Government is underplaying the true extent of pollution in the UK.
"With a new batch of MPs, at least 181 of whom appear to have high levels of pollution in their constituency, and a new Environment Secretary, there can be no excuse for weak action as ministers pull together the final air quality plan over coming weeks.
"These results, and the stories behind them of people suffering poor health because of air pollution, add even more weight to the overwhelming case for quicker, tougher action on dirty air."
A Defra spokeswoman said: "Improving the UK's air quality and cutting harmful emissions is a priority for this government.
"That's why we have invested more than £2 billion since 2011 to increase the uptake of ultra-low emissions vehicles, support greener transport schemes and set out how we will improve air quality through a new programme of clean air zones."