North Lanarkshire's trading standards watchdogs have found that nearly half of the MOT test centres tested in the region were passing cars deemed not roadworthy.
According to a report from the Wishaw Press, five out of the ten outlets passed vehicles that had either damaged headlights or illegal tyres.
In these instances, qualified engineers had doctored many vehicles to appear non-faulty before they were submitted.
Speaking to the news provider, trading standards manager Dave Roderick called on any driver or small business that was suspicious of MOT test practices to come forward.
"Any consumers who feel that they have, despite our project results, been unfairly treated should contact my colleagues and we will investigate their concerns," he said.
The news comes after a recent survey from Office of Fair Trading-backed Motor Codes showed that the most complaints against garage service quality were occurring in London and the south-east, which accounted for a third.