In the case of ClientEarth v Secretary of State for the Environment, Food and Rural Affairs, the Supreme Court delivered a landmark unanimous judgment on 29 April.

The case concerned the UK's continued failure to comply with mandatory nitrogen dioxide limits by the due dates set by EU air quality directives. Failure to do so had been challenged by the environmental NGO ClientEarth, and questions of EU law had been referred to the European Court of Justice, and back to the Supreme Court with authority to take "any necessary measure" to deliver compliance with EU law.

While taking note of the complex contributory factors to failures of EU air quality legislation, such as the ineffective Euro 1-5 diesel car emission standards, and the fact that many EU Member States have similar problems, the Supreme Court noted that UK compliance was out of time and many years overdue.

Lord Carnwath, delivering the judgment of the Court, made a mandatory order requiring the Secretary of State to prepare new air quality plans, in accordance with a defined timetable, and to deliver them to the European Commission no later than 31 December 2015.

The Supreme Court's order will apply to the new government taking office after the General Election on 7 May.

Read the The Supreme Court order.