The Government has lost its bid to delay publication of its long-awaited air pollution plan.
A judge at London's High Court ordered the draft Air Quality Plan to be published on 9 May, the week after the local elections, with the final plan out on 31 July.
Environment Secretary Andrea Leadsom told Parliament that pre-election proprietary rules, commonly known as purdah, meant it would be inappropriate to publish the plan before the General Election.
A lawyer acting for Defra argued the plan would drop a "controversial bomb" on both local and national elections.
They claimed it would be more efficient to delay publication in case the new government wanted to make changes to the draft.
But ClientEarth, an environmental law firm which brought the case, disagreed.
It told the court: "This is a huge focus of public concern and a huge issue for the media.
"It is an issue in this election, whether the Government publishes the consultation or not.
"The controversy is there and is not going to be put on hold by not publishing the consultation document."
It argued that while the rule of purdah could be applied to the local elections, it was not in this case relevant to the General Election.
The judge, Mr Justice Garnham, accepted their claims, concluding that "Purdah is not a trump card to be deployed at will" and adding that "purdah does not mean it is not possible to publish a plan".
He found that the public health argument outweighed other factors in reaching his decision, quoting Defra's own figures which show that 23,500 people die each year as a result of air pollution.
"There is a powerful case and there are exceptional circumstances that make publication essential," he added.
ClientEarth chief executive James Thornton said he was "delighted" with the decision.
"We cannot afford more dither and delay from the government," he said.
"Rather than appeal this decision, they need to get on and produce their plans to bring down air pollution as soon as possible.
"The judge agreed with us that this is a matter of public health, not politics," he added.
The issue of air pollution has been going on for some time. Seven years ago, Britain was told it was in breach of the legal limits of toxic gases such as nitrogen dioxide.
Two years ago, the Government was ordered to come up with a plan to tackle air pollution.
In November last year, ministers were told it did not go far enough and were given another deadline to draft a new plan.
Dr Penny Woods, chief executive of the British Lung Foundation, said: "The nation's dirty air is one of the most important public health issues in recent times, and the High Court's decision recognises the need to urgently tackle this crisis.
"Toxic air left unchecked will lead to a rising tide of ill health for everyone, particularly those who are most vulnerable.
"Children, people with a lung condition and the elderly will be hit hardest."
The Government said it would seek grounds to appeal against the ruling.