The Driver and Vehicle Standards Agency (DVSA) has revealed that one in 12 lorries checked by its examiners were fitted with emissions fraud devices.

The most common type of device found is an ‘emulator’, which stops the lorry’s existing emissions control system from working.

According to the DVSA the devices are fitted by ‘unscrupulous’ drivers and operators in order to cut the cost of maintenance and repairs.

Gareth Llewellyn, DVSA chief executive, said: “DVSA’s priority is to protect you from unsafe drivers and vehicles. We are committed to taking dangerous lorries off Britain’s roads. Stopping emissions fraud is a vital part of that.

“Anyone who flouts the law is putting the quality of our air and the health of vulnerable people, at risk. We won’t hesitate to take action against these drivers, operators and vehicles.”

Between August, when the new checks started, and the end of November, DVSA examiners inspected 3,735 lorries on strategic routes, including those entering and leaving Britain, and found 293 with emissions fraud devices fitted.

Examiners found illegal devices fitted to 151 vehicles registered in Great Britain, out of 1,784 checked and 60 vehicles from Northern Ireland, out of 294 checked.

Vehicles from outside the UK fared better, with 82 out of 1,657 fitted with devices.

Drivers or operators of these vehicles have to remove the devices within 10 days. Those that continue to operate vehicles that haven’t been fixed face a £300 fine and will have their vehicle taken off the road. But they also risk losing their licence to operate a haulage business altogether - and with it their livelihood.

Senior Traffic Commissioner, Richard Turfitt, added: "Traffic Commissioners welcome the steps being taken by the enforcement agency to identify emissions cheats. Use of these devices threatens to undercut responsible and compliant operators as well as damaging the environment and public health.

“We will look to take action wherever an operator seeks an unfair and illegal advantage over the rest of industry."