The MOT test for cars with diesel engines is set to become much tougher from February 2014 due to new rules about exhaust filters.

Diesel-engined cars fitted with an exhaust filter as standard when new will now be checked to make sure it is still present.

Any car found to have had the filter removed will be automatically failed and required to have a new filter fitted.

The filter is there to trap harmful diesel particles that would otherwise be released into the environment.

Some drivers have the filter removed because they think it will improve fuel economy or to save the cost of a replacement.

However, it is now an offence to drive a car with the filter removed as it no longer meets emissions standards.

Roads minister Robert Goodwill said: "I am very concerned that vehicles are being modified in a way that is clearly detrimental to people's health and undoes the hard work by car makers to improve emissions standards.

"It has become apparent that Government had to intervene to clarify the position on particulate filter removal given the unacceptable impact on air quality.'

Diesel particulate filters need to be brought up to full working temperature regularly on a longer drive so they can burn off the soot that collects in them. This ensures they work properly and last a long time.