Nearly 90% of tyres replaced by ATS Euromaster were below the legal tyre depth limit.
According to the firm’s Manchester branch manager, the tyres pose a safety risk when the tread falls below 1.6mm.
The manager of the branch in Manchester, Paul Duff, said that tyre safety has got worse over the last five years thanks to more vehicles having low-profile tyres, pushing up replacement costs.
Duff also said that customers are not checking tread depths on a regular basis, or at all.
The tyre-fitting company warned that if a tyre’s steel cord is visible, the tyre risks losing its structure with every rotation as it is the only part of the vehicle that it is in contact with the road surface.
“It’s a ticking time bomb waiting to go off,” Duff said.
“A lot of people don’t realise, but if you’re involved in an accident and are found to have an illegal tyre on your car then you risk your insurance policy being declared void, because your vehicle is illegal for road use,” he added.
Department for Transport statistics from 2013 show that illegal, defective or underinflated tyres were the most common vehicle defect contributing to accidents in Great Britain where a police officer attended the scene.