The Government is to be sued for a third time over its plan to bring air pollution to within legal safety limits by legal activist group ClientEarth, which said there were “major flaws” in its latest attempt.

The group said, after examining the Air Quality Plan, it had written to the Department for Environment, Food and Rural Affairs (Defra) asking for a number of improvements. They said Defra’s refusal had left them with no option but to return to court.

ClientEarth has twice successfully won court orders requiring the Government to produce better plans to tackle air pollution.

Ministers had attempted to delay publication of their third attempt at a plan that complied with European Union law until after the election, with their lawyer arguing it would drop a “controversial bomb” on the campaign.

Environment Secretary Andrea Leadsom also cited the pre-election period of purdah in which government officials cannot comment on political issues outside of “emergency” matters, tacitly suggesting she did not regard air pollution as a pressing issue.

The judge decided that neither was a good enough reason to breach the court order, saying ministers had a duty to abide by rulings like anyone else.

But James Thornton, chief executive of ClientEarth, made clear they were unimpressed by the resulting draft document, which suggested local councils should take the lead in reducing air pollution, rather than the Government.

“We have found some major flaws. The law requires the final plan to bring air pollution down to legal levels in the shortest time possible. These flaws seriously jeopardise that timetable,” he said.

“These are plans for more plans, what we need are plans for action.”

The draft plan is subject to a public consultation, which will end just a week after the general election, with the actual plan due to be published by the end of July.

“The Government’s plans and consultation do not match what its own evidence says needs to happen,” Mr Thornton said.

“If the evidence shows that taking certain measures will be necessary to tackle the public health crisis of polluted air, then the plans and associated consultation need to make that clear.

“This is essential so that people can have their say and we get the best possible final plans when they are due to be published, as ordered by the court, on 31 July.”

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ClientEarth has called for incentives to prompt motorists to switch from using diesel vehicles to cleaner forms of transport.

It urged people to let the Government know their feelings on the subject and has launched its own “online consultation tool” to help them do so.

Mr Thornton added: “We are challenging on two fronts because of the urgency of this public health crisis.

“We’re asking the High Court to consider the problems with the plans and consultation. That is now in the court’s hands.

“In the meantime, it is important for as many people as possible to tell Defra that the plans don’t make sense and won’t tackle illegal air quality in our towns and cities.”

Areeba Hamid, a clear air campaigner with Greenpeace, said it was “disgraceful” that the Government needed to be “dragged back to court so many times over for failing to tackle illegal and unsafe air pollution that’s plaguing our streets”.

“Our air has broken legal limits for pollution every year since 2010, and yet the Government is still not acting to protect the public from this crisis,” she said.

“By delaying action to tackle air pollution over and over again the Government is putting people’s lives at risk, and the voting public will expect better.

“To tackle the UK’s air pollution crisis, we need to tackle diesel vehicles. Even the newest diesel cars on our roads are pumping out a lot more pollution than is allowed.

“The car companies cheated at emissions tests, and now we’re paying the price with our health. The Government must get to grips with diesel, and tackle the car companies head on.”