The UK, along with five other nations, have been referred to the European Court of Justice after they have failed to tackle high levels of air pollution.
In January, the UK, France, Germany, Hungary, Italy and Romania were all given a final warning by the European Commission.
If the countries in question do not act quickly to improve their air pollution problems the European Court of Justice is able to impose multimillion Euro fines.
In February, UK courts pressured Ministers to improve plans that they described as "woefully inadequate" after losing in the high court for the third time to environmental lawyers.
Air quality has been an increasing problem in the UK, with EU-set limits on key pollutants breached frequently, and Ministers have been slow to address the problem.
Many believe that "clean air zones", are not being implemented widely, or quickly enough to prevent the Government's own commitments on clean air from being breached.
Air pollution results in over 400,000 early deaths across Europe every year, according to the Royal College of Physicians and the Royal College of Paediatrics and Child Health.
A senior doctor, Prof Neena Modi, said:
"Having been told [by the courts] to go back to the drawing board so many times, that the Government's final air quality plan still lacks sufficiently strong measures to clean our air is frankly inexcusable".
The limits set out on air pollution under Directive 2008/50/EC on ambient air quality and cleaner air for Europe, had to be met in two stages, but they are still being breached by the six nations.
A statement from the Commission said that the six Member States have failed to deliver "credible, effective and timely measures to reduce pollution as soon as possible, as required under EU law".
The Czech Republic, Slovakia and Spain all received a final warning but have since delivered appropriate new measures.
The European case will now go to the European Court of Justice, which will hold a hearing in the coming months. If the UK is found to be in breach of its legal duty, it will be given a period of time to resolve this. If no resolution is found, the court will then be able to impose huge fines.
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