The UK’s highest court has sent a shiver through the diesel car industry by ordering the government to show it is serious about tackling the air pollution that blights London and other cities.

In a unanimous judgment, the Supreme Court said the government must speed up efforts to meet European pollution standards and submit new air quality plans to Brussels no later than December 31, regardless of the May 7 general election outcome.

“The new government, whatever its political complexion, should be left in no doubt as to the need for immediate action to address this issue,” the court ruled.

The move stems from an EU air quality directive that gave the UK until 2010 to curb traffic fumes that are a leading source of nitrogen dioxide, or N02, a harmful gas linked to heart attacks and asthma.

The government said it could take until 2030 before N02 levels meet EU standards in several cities, including London, prompting a five-year legal battle with ClientEarth, an environmental law group that launched a case to hasten action.

ClientEarth lawyer Alan Andrews said Wednesday’s ruling would save thousands of lives and could have implications for plans to expand sites such as Heathrow airport.

“The next government will have to carefully consider the impact of all major projects, including airports, on nitrogen dioxide levels, particularly in light of the legal requirement to achieve limits in the shortest time possible,” he told the FT.

A Heathrow spokesperson said the airport was a “small but material contributor to air pollution levels in the area” but non airport traffic and pollution blown in from London and the rest of the UK was a much bigger source.

The ruling is likely to add to what the car industry feels is a “creeping demonisation” of diesel cars, which have been heavily promoted under various government initiatives and now make up about a third of passenger cars on Britain’s roads.

The vehicles emit less carbon dioxide in exhaust fumes than petrol equivalents but are also a source of N02.