The European Commission is taking the British Government to court for breaching EU air quality rules.
The EU's environment commissioner Karmenu Vella said Britain had broken limits on levels of health-damaging nitrogen dioxide (NO2) and failed to provide "credible, effective and timely" plans to cut pollution.
Levels of NO2 - largely from car exhaust fumes - peaked as high as 102 microgrammes per cubic metre of air in 16 locations in the UK in 2016, including London, Birmingham, Leeds and Glasgow, compared to an EU limit of 40 microgrammes.
The European Commission also issued a letter of formal notice to the UK for disregarding EU measures to deter car manufacturers from trying to cheat emissions tests, introduced in the wake of the Volkswagen diesel scandal.
France and Germany were also referred to the European Court of Justice for breaching NO2 limits, though neither reached the pollution levels of the UK, with 82 microgrammes per cubic metre recorded in Stuttgart and 96 in Paris.
Mr Vella said: "The decision to refer member states to the Court of Justice of the EU has been taken on behalf of Europeans.
"We have said that this Commission is one that protects. Our decision follows through on that claim.
"The member states referred to the Court today have received sufficient 'last chances' over the last decade to improve the situation.
"It is my conviction that today's decision will lead to improvements for citizens on a much quicker timescale."
Warning that legal action alone will not solve the pollution problem, Mr Vella also unveiled a raft of new Commission measures to help member states promote cleaner air.
The Department for Environment, Food and Rural Affairs (Defra) said the UK was one of 22 EU states exceeding NO2 limits.
It said the main reason for non-compliance was the failure of European standards for diesel cars to deliver the expected reductions in emissions.
A Defra spokesman said: "We continue to meet EU air quality limits for all pollutants apart from nitrogen dioxide, and data shows we are improving thanks to our efforts to bring levels of NO2 down.
"We will shortly build on our £3.5 billion plan to tackle roadside emissions with a comprehensive Clean Air Strategy setting out a wide range of actions to reduce pollution from all sources."
Green Party co-leader Caroline Lucas welcomed the Commission action.
"This announcement is good news for all those suffering from chronic air pollution," said Ms Lucas.
"People have been breathing in toxic air for too long because of the failure of the British Government in tackling this issue.
"Indeed this announcement from the European Commission is an extremely powerful reminder of just how much we'd miss the EU enforcement powers when it comes to environmental protection if Brexit happens.
"The current plans by the Government to enforce these kind of rules are simply not up to the task - and they clearly need an urgent rethink to ensure environmental protection isn't sacrificed as we hurtle towards Brexit."