Environment lawyers are expected to take the government back to court over its controversial plans to tackle the UK’s air pollution crisis. They say the proposals are so weak they flout ministers’ obligation to protect public health.

The government published its plans to cut levels of diesel fumes, nitrogen oxides and particulates in the atmosphere on Friday – after being forced by judges to act on the crisis. Medical experts say toxic air is responsible for tens of thousands of premature deaths every year.

The plans by the government contained little concrete detail and left most anti-pollution measures to be dealt with by local authorities. “These belated proposals are toothless and woefully inadequate,” said the mayor of London, Sadiq Khan.

James Thornton, founder and chief executive of ClientEarth, was equally caustic. “The more we study this appalling plan, the more unsatisfactory it gets,” he said.

His organisation took the government to the supreme court to force it to comply with its legal obligation to reduce air pollution. Ministers had claimed they were not obliged to act on the issue as a matter of urgency. The court disagreed and told them to produce an air pollution plan as a priority. When this plan was published in 2015, it was deemed to be so poor it was illegal and the government was told – by the high court – to submit a new plan by April.

A few days ago the government used the excuse of the general election to postpone publication of this latest plan. Once again, it was taken to court by ClientEarth, where ministers were told they could not postpone publication. On Friday, they produced their report, to general derision and a growing conviction that environmental lawyers will demand far more robust action to deal with air pollution.

“This latest plan is even worse than the previous effort, which has already been ruled illegal by the high court,” said Thornton. “The government should be ashamed of itself. It has dragged its heels for seven years while we choke on illegal and poisonous air; it’s been hauled through the supreme and high courts and had to be forced by a judge to publish this delayed plan.

“We need to ask ourselves at what point will the government take this public health emergency seriously enough to start protecting our health and our children’s futures, instead of the car companies?

“The government must, and will be forced to, obey its own laws to protect our health and give us safe and cleaner air to breathe.”