Environmental lawyers have launched a new legal challenge to force the Government to act on air pollution.
ClientEarth, which won a ruling against the Government in the Supreme Court over its failures on air pollution last year, says the Environment Department's (Defra) recently published plans to cut pollutants fall "woefully short" of what the court ordered.
The law firm has lodged papers with the High Court seeking an order striking down the Government's air quality plans and ordering new ones.
The move comes after a report from the Royal College of Physicians and the Royal College of Paediatrics and Child Health warned an estimated 40,000 people die early each year in the UK because of air pollution.
European rules set limits for key pollutant nitrogen dioxide (NO2) which should have been met by 2010, but ClientEarth said the plans which the Government was ordered to produce by the Supreme Court do not see the UK meeting legal targets until 2025.
The "air quality plan" published late last year focused on bringing in clean air zones in five English cities by 2020, in which the most polluting buses, taxis, coaches and lorries will be charged to enter the centre.
But the move does not cover private cars, which ClientEarth said are one of the biggest sources of poor air quality in cities.
London, which breached its air pollution limits for NO2 for the whole of 2016 just a week into January, is set to introduce a ultra-low emission zone in London by 2020 which will cover all vehicles, but is not expected to meet legal levels until 2025.
ClientEarth lawyer Alan Andrews said: "The Government has repeatedly failed to tackle this problem, despite a ruling by the Supreme Court.
"As the Government can't be trusted to deal with toxic air pollution, we are asking the court to intervene and make sure it is taking action.
"Tens of thousands of early deaths are caused by air pollution every year. It is a disgrace that we have had to take further legal action to force the Government to protect our health.
"The Government's plans were an insult to those being made sick and dying from air pollution and failed to consider strong measures to get the worst polluting diesel vehicles out of our town and city centres."
Dr Penny Woods, chief executive of The British Lung Foundation, said: "First time the Government was taken to court over air pollution, they agreed to introduce the Clean Air Zones we'd campaigned for.
"Maybe this time they'll take up our idea of monitoring pollution outside schools to protect children.
"40,000 people die each year in this country as a result of air pollution. It's a public health emergency; the Government must act now, not wait to be dragged through the Courts again."
A spokeswoman for the Environment Department (Defra) said: "Our plans clearly set out how we will improve the UK's air quality through a new programme of Clean Air Zones, which alongside national action and continued investment in clean technologies will create cleaner, healthier air for all."