The Commission also referred France, Germany, and the United Kingdom to the Court of Justice of the European Union for failure to respect limit values for nitrogen dioxide (NO2), and for failing to take appropriate measures to keep exceedance periods as short as possible.
In a statement sent to Post&Parcel, ClientEarth's CEO James Thornton said: "On top of our three successful cases, today's legal action from the European Commission is more damning evidence of the mountain the United Kingdom government still has to climb to bring air pollution to within legal limits".
Their proposed measures were rated by the Commission as sufficient for the time being to tackle the identified gaps.
"We can not wait any longer", Vella said, warning that Brussels may end up waiting several more years before the countries put measures in place.
"We can not wait any longer", he added.
The commission has been urging the wayward member countries to establish incentives for the transport, energy and agricultural sector as well as improve urban planning and building design. Air pollution requires urgent action and it's been clear for too many years that authorities all across Europe are failing to protect their people from illegal and harmful levels of air pollution.
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. Action is also being taken against France, Germany, Italy, Hungary and Romania.
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Environment ministers from some of the EU's worst air pollution offenders have been summoned to Brussels for an end-of-month meeting with the European Commission, where they will have to answer some tough questions.
The European Commission has had enough of being ignored by what has been dubbed a "toxic bloc" of countries. "The countries being sent to court have had too many final warnings".
"We call on the Commission to continue show its full commitment to improve air quality in Europe and swiftly pursue all countries in breach of air quality laws".
But she added that the process behind legal action should be "far more transparent" to allow citizens to know why some countries are taken to court and others not.
"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 NO2 levels were mostly produced by diesel cars and the No 10's plan in 2017 was condemned as as "woefully inadequate" by city leaders and "inexcusable" by doctors.