The government's failure to meet EU standards on air pollution is "putting the health of UK residents at risk", says the Environmental Audit Committee.
Bad air quality costs the nation £8.5-20bn per year via poor health, it says, and can cut life expectancy by years.
Continued failure to meet EU standards could result in swingeing fines.
The committee says ministers' "apparent tactic" to avoid fines is to ask the European Commission for repeated extensions rather than curb pollution.
The government's latest request to the commission - to delay having to meet standards on nitrogen dioxide (NO2) until 2015 - is being taken to judicial review by environmental lawyers ClientEarth.
By some measures, the UK has been in breach of EU rules since 2005, the committee's report notes.
It last reported on air pollution 18 months ago, and says that since then, there is "no meaningful evidence" to suggest progress towards meeting standards.
Yet evidence on the health impacts, it says, has become clearer.
Nationally, the government accepts that air pollution takes seven or eight months off Britons' life expectancy. But for the 200,000 people most directly affected, the shortfall is two years.
"It is a national scandal that thousands of people are still dying from air pollution in the UK in 2011 - and the government is taking no responsibility for this," said committee chair Joan Walley MP.
"It is often the poorest people in our cities who live near the busiest roads and breath in diesel fumes, dangerous chemicals and bits of tyre every day."
Recent UK research indicated that tyres and brakes are a significant source of airborne particles, in addition to vehicle exhausts.
'Not taken seriously'
On particulates, the UK is improving. Six years ago, eight places in the country exceeded EU standards.
Now, only London does; but the London picture is startling. EU regulations allow legal limits to be exceeded for 35 days per year. This year, the quota was reached in April.
A more problematic area is nitrogen dioxide. Currently, 40 out of 43 "assessment zones" across the country exceed the EU standard.
The government's own projections, released in June, indicate that 17 will still be in breach in 2015, with Greater London taking even longer to clean up, despite the avowed intention of everyone connected with the Olympics to make them the "greenest games ever".
Government plans for curbing NO2 pollution include financial incentives for switching haulage from road to rail, research on how retailers could deliver goods outside peak times, and differential pricing for vehicles emitting lower levels of pollutants.
And the London administration of Mayor Boris Johnson has set age limits for black cabs, invested in cycling, and implemented the London Low Emission Zone.
The Environmental Audit Committee says that even so, the air pollution issue is just not taken seriously in government.
"There are no air quality actions for Defra or the Department for Transport in their departmental business plans," it says, and few government departments "appear to understand the importance of the issue".
A spokeswoman for the Department of Environment, Food and Rural Affairs said the government was working towards full compliance with EU standards, and that significant progress had been made.
"We are investing significant sums of money to facilitate further reductions in pollution around transport, including over £1bn to promote the uptake of ultra low emission vehicle technologies and to support local transport authorities to deliver sustainable transport measures," she said.
"We welcome the committee's continued interest in this work, and we will fully consider their recommendations before providing a written response in due course."
The government's response to the committee' previous report was rooted in the localism principle, with responsibility being devolved downwards to local authorities.
The committee warns that this could mean EU fines being passed down to local authorities as well.
"Under the banner of its localism agenda, the government is dumping the problem on local authorities who simply do not have the resources to tackle what is a national problem," said Alan Andrews, air quality lawyer at ClientEarth.
"It is simply putting off taking action while behind the scenes it lobbies the EU to weaken limits."
The committee says government should urgently implement incentives to retrofit old vehicles with equipment to reduce pollution and set up a network of Low Emission Zones in the worst-affected areas.
And it warns that meeting the NO2 standard would be impossible in the event of a third runway being constructed at Heathrow - an option that is currently ruled out by Coalition policy.
The committee's call to action is partly couched in historical terms; air pollution in London causes as many deaths now as in the bad old days of the "pea-souper" smogs, it calculates.
"It is estimated that around 4,000 people died as a result of the Great Smog of London in 1952. That led to the introduction of the Clean Air Act in 1956.
"In 2008, 4,000 people died in London from air pollution and 30,000 died across the whole of the UK.
"The government needs to act now, as government did in the 1950s, to save the health of the nation."
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