The Supreme Court of the United Kingdom that is! Last week they delivered a judgement that requires the incoming government to draw up plans to reduced the levels of certain air pollutants to an already agreed maximum. This was the announcement which explains the background as well as giving the judgement. (Unlike the USA, only the Supreme Court is regularly broadcast and video available on YouTube). Please note that at 2:02, Lord Carnwath refers to “31 January 2015” when this should be read at “31 December 2015”
More official details are most accessible in the press summary (.pdf) provided by the court. The Guardian provides an easier to understand summary of the case:
London and several other British cities have failed to meet EU standards on nitrogen dioxide (NO2) levels since 2010, running the risk of fines from Brussels [the EU Commission] and prompting a legal challenge by NGO ClientEarth.
On Wednesday, five judges unanimously ruled in the group’s favour and said the next environment secretary must draw up a plan to meet the EU rules by the end of 2015
The main cause of the hotspots is the use of diesel powered vehicles. These have been promoted by successive governments by reduced vehicle and fuel taxes due to the fuel efficiency and the relative lower emissions of carbon dioxide. Unfortunately they produce considerably more nitrogen dioxide which is injurious to human health. New EU emission standards for vehicles have been produced but makers have yet to produce a full range of "Clean diesel" engines. The iconic London black taxis are all diesel driven as were buses previously. Transport for London has introduced the "new Routemaster" bus which is a diesel/electric hybrid. Other newer buses are hybrid and hydrogen powered. Oxford Street in London is one of the worst places in Europe for the levels of NO2. This is mostly because only buses and taxis are allowed to travel down its whole length, all of which in one way or another use diesel fuel. Reductions should progress as the entire bus fleet moves away from pure diesel power.
This judgement is notable as being the first to bind an incoming government to make policy decisions. The plans must be sent to the EU commission by the end of the year. (R is "Regina" so the case was the Queen vs the Secretary of State, even though the case was brought on an application by ClientEarth)