Hopes for expanding Heathrow Airport were said to have been dealt a 'major blow' today, after the UK's Supreme Court assumed responsibility for enforcing EU pollution law.

Nitrogen Dioxide levels at the airport are already in breach of the EU Air Quality Directive, although management blame traffic on the M4.

The government had attempted to avoid a showdown with the EU by agreeing to reduce pollution levels in line with the directive by 2025, but the date has since slipped to 'post 2030'.

The Court of Justice of the EU (CJEU) has now rejected this plan and UK ministers will have to prepare new measures for reducing illegal pollution levels 'as soon as possible'.

The CJEU has given the Supreme Court responsibility for enforcing compliance with air quality law. Judges will examine the case next year.

The cross-party 2M group of councils opposing expansion says this is a 'major blow' for the plans.

Hillingdon Council leader Councillor Ray Puddifoot, a spokesman for the group, said: “Before this ruling Heathrow believed it had over a decade to meet the legal pollution limits. Even then the airport was making some highly optimistic assumptions about cleaner aircraft being invented and then rushed into service.

“There is no way out of this for Heathrow. Ministers may have given them an easy ride but now the Supreme Court will have to be convinced pollution will be reduced 'as soon as possible' while increasing flights, road traffic and freight.”

Building a third runway would increase the annual number of flights at the airport from 480,000 to 740,000, while the freight operation would double in size, as would the number of people using the airport.

But Heathrow's management say the ruling will have 'no impact' on their plans for expansion.

A spokeswoman said: “We take air quality very seriously and have always said we will only go ahead with Heathrow expansion if we can do so within strict air quality limits.

“Within two kilometres of the airport, the only air quality monitoring site to exceed the EU limit value for NO2 [nitrogen dioxide] is located alongside the M4. The results at that location are largely as a result of road traffic, approximately three quarters of which is not airport-related.

“In the last decade Heathrow has achieved significant reductions in emissions – even though the numbers of people and aircraft using Heathrow have increased. This is due to a number of unique initiatives to reduce local air pollution in Heathrow, including by promoting public transport options by funding the UK’s largest free travel zone, the use of more sustainable vehicle options through our Clean Vehicles Programme, hosting the UK’s first publicly accessible hydrogen refuelling site, and having one of Europe’s largest electric airside vehicle fleets.

“In recognition of its work to improve local air quality, Heathrow Airport has recently won the title of greenest business of the year at the 2014 West London Business Awards.”