Thousands of diesel cars still on the roads with vital pollution filters removed

File photo dated 02/02/07 of a car exhaust. Parents who leave their car engines running while on the school run should face fines as part of a drive to cut air pollution, new guidance suggests.

All diesel vehicles built since 2009 have been fitted with a pollution-busting particulate filter. This cuts harmful emissions from the exhaust by up to 95 per cent, but they have a tendency to go wrong, clog up and cause breakdowns – at which point unscrupulous motorists often have the filters removed rather than paying for a costly repair.

An investigation by BBC Radio 5 Live found that the Driver and Vehicle Standards agency has caught 1,800 cars running without these vital filters in the last three years – but experts say that figure is likely to be significantly higher, and could be contributing to worsening air quality in towns and cities.

That's because MoT examinations do not test for the presence of a particulate filter. Instead, a cursory visual inspection allows modified vehicles to pass through undetected. In fact, the radio station tested this out by removing the filter from a car and taking it to three MoT test centres. The car passed all three.

Mary Creagh, chairwoman of the Commons environmental audit committee, said: "I'm concerned there could be tens of thousands of cars on the road which have had these filters removed. The government should tighten MoT tests and close the legal loophole that allows garages to remove them and cheat the public out of clean air."

Nick Molden, CEO of Emissions Analytics, agreed. "The MoT test is clearly not fit for purpose in checking if a filter has been removed."

But just how damaging is a car without a filter? A notice issued to MoT testers in 2014 said: "The DPF (diesel particulate filter) plays an essential environmental role in enabling reductions in emissions, reducing air pollution and thereby improving health quality."

Poor air quality is associated with 40,000 premature deaths a year in the UK. Frank Kelly, professor of environmental health at King's College, London, described the health impact as devastating. "If a filter is removed, it takes the work being done to restrict emissions back 30 years," he told the BBC. "The particles lead to numerous health problems such as lung cancer, heart attacks, strokes, Parkinson's, Alzheimer's, and can also affect an unborn child in the womb."

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