Hundreds of lorries found to cheat emissions tests
One in 13 examined as part of Government crackdown were fitted with cheat devices.
One in 13 lorries examined as part of a Government crackdown on air quality violations were fitted with cheat devices.
The Driver and Vehicle Standards Agency (DVSA) said unscrupulous drivers and businesses use emulators to stops a lorry's emissions control system from functioning in an effort to cut the cost of maintenance and repairs.
DVSA examiners found devices fitted on 293 out of 3,735 lorries in the first four months after new checks were introduced in August last year.
There were 151 registered in Britain, 60 from Northern Ireland and 82 from outside the UK.
Drivers or operators of vehicles caught out have to remove the devices within 10 days or face a £300 fine and having the vehicle taken off the road, with firms also risking the loss of their licence to operate a haulage business.
Volkswagen sparked outrage in September 2015 when it was found to have fitted defeat device software to 11 million diesel vehicles worldwide.
This allowed the manufacturer to cheat tests for nitrogen oxide pollutants.
Air pollution causes an estimated 40,000 premature deaths a year in the UK and is linked to health problems from childhood illnesses to heart disease and even dementia.
DVSA chief executive Gareth Llewellyn said the agency's priority is to protect the public from unsafe drivers and vehicles.
"We are committed to taking dangerous lorries off Britain's roads," he said.
"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."
Natalie Chapman, a policy chief at the Freight Transport Association, said any drivers caught trying to cheat air quality standards should be "punished to the full letter of the law".
"A small handful of unscrupulous operators, which DVSA has identified through targeted enforcement, should not be allowed to tarnish the reputation of the wider freight industry, which has made huge strides in reducing emissions in the past few years," she said.