Britain's government must publish proposals to tackle air pollution months earlier than it wanted, a top court ruled Thursday, saying the plans cannot be delayed until after June's general election. 

Moves to address illegal levels of nitrogen dioxide pollution -- largely caused by diesel emissions -- must be unveiled by May 9, a High Court judge said, drawing praise from campaigners.

"We're delighted with today's decision. We have said that this is a public health issue and not a political issue," Anna Heslop, clean air lawyer for ClientEarth, which brought the case against the government, told AFP.

Environmental pressure group Greenpeace also welcomed the verdict, saying the court had "called out the government on its underhand dodging of the air pollution crisis".

But lawyers representing the government maintained that such publication would drop a "controversial bomb" as voters head to the polls for the election called by Prime Minister Theresa May.

The High Court had initially demanded the government publish its plan by April 24, but ministers applied to the courts for the release to be postponed until September 15, due to the June poll.

A Downing Street spokeswoman said on Thursday that the government "will consider the judgement and decide what to do next".

Air pollution contributes to the deaths of more than 40,000 people per year in Britain, according to official figures, with nitrogen dioxide a particular problem.

Source: AFP