Almost two thirds of Britons are living in areas with illegal levels of air pollution, new analysis has revealed.

Nearly 40 million citizens live in towns and cities where the levels of harmful nitrogen dioxide (NO2) are above legal limits set by the EU.

The study commissioned by the Labour Party raises fresh concerns over the public health impact of air pollution, after a string of findings linked poor air quality to disease and early death.

Sue Hayman, the Shadow Environment Secretary, called the levels of air pollution a “national crisis”.

“Labour will not allow the Tories to use the snap general election or Brexit to kick this issue into the long grass, or water down standards that would put millions of UK adults and children at risk,” she told The Guardian.

Her party said it would introduce a number of “clean air zones” across the UK and fight to close loopholes in car emissions tests if elected.

The new data reveals 59 per cent of people in the UK are living amid illegal pollution levels. Towns and cities including Aberdeen, Birmingham, Bournemouth, Burnley, Leeds and Sheffield all breach NO2 limits, as do many areas of London.

In the capital alone, NO2 pollution, which is caused mostly by diesel vehicles, is responsible for 5,900 early deaths each year.

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Under the EU’s legally-binding Air Quality Directive, levels of NO2 should not exceed 40 micrograms per cubic metre of air.

The news came as government ministers made a last-minute bid to delay a High Court deadline for submitting revised proposals for tackling air pollution.

The Government had been ordered to produce tougher measures by 4.00pm on Monday after their initial plan was dismissed by judges on the grounds it was so weak that it was unlawful.

At 7.00pm on Friday, ministers requested a lengthy delay that would allow them to hold off putting forward new plans until after the 8 June general election.

A spokesman for the Department for Environment, Food and Rural Affairs said: “We are firmly committed to improving the UK’s air quality and cutting harmful emissions. We are seeking an extension to comply with pre-election propriety rules.”

But Greenpeace UK said there was “no excuse” for further delaying the publication of the plan.