The European Commission has issued “final warnings” to five countries, including the UK, for failing to address air pollution.
It said the UK, along with Germany, France, Spain and Italy, have repeatedly breached air pollution limits for Nitrogen Dioxide (NO2).
The pollutant poses serious health risks, with most emissions resulting from road traffic.
It is urging all five Member States to take action to ensure good air quality and safeguard public health.
Air quality standards in 23 out of 28 Member States are still being exceeded – in more than 130 cities across Europe.
To date, legal action on NO2 involves 12 countries, with ongoing infringement cases against Austria, Belgium, the Czech Republic, Denmark, France, Germany, Hungary, Italy, Poland, Portugal, Spain and the UK.
The Commission says action against other Member States may follow.
The UK Department for Environment, Food & Rural Affairs (Defra) insists the government is “firmly committed” to improving air quality and cutting harmful emissions.
A spokesperson added: “That’s why we have committed more than £2 billion since 2011 to increase the uptake of ultra-low emissions vehicles and support greener transport schemes and set out how we will improve air quality through a new programme of Clean Air Zones. In addition, in the Autumn Statement, we announced a further £290 million to support electric vehicles, low emission buses and taxis and alternative fuels.
“We will update our air quality plans in the spring to further improve the nation’s air quality.”
The European Court of Auditors are checking the effectiveness of EU and national measures to reduce air pollution and assessing whether funds are being spent “wisely”