Tests for diesel cars and lorries are to be tightened up to ensure vehicles have a critical exhaust filter if one had originally been fitted as standard.

Garages and testing stations will be required to check for a diesel particulate filter (DPF) in the inspection of the exhaust system as part of the MoT test (or annual test for heavy vehicles) from February 2014.

The vehicle will automatically fail the MoT test if the filter had been fitted as standard but is found to be no longer present.

The filter works by trapping solid particulate matter from exhaust gases. This type of filter has been in use for more than 20 years and helps meet European emission standards, improving air quality and health standards.

Some firms offer services to remove the filter, claiming it will reduce fuel consumption. But it is an offence to drive a vehicle that has been modified this way, as it will no longer meet the emissions standards it achieved when approved for sale in the UK.