Dangerous second-hand tyres are putting motorists' lives at risk, councils have warned - with a local authority finding one such tyre stocked to be 23 years old.
As many as 83% of used tyres in some areas are being sold illegally, the Local Government Association (LGA) said.
Part-worn tyres are being sold with serious safety defects, unsafe repairs and incorrect labelling, according to council Trading Standards teams.
Durham County Council officers found that only one out of 39 (2.6%) tyres stocked at various dealers bore the required "part-worn" tyre marking, with 25 tyres having problems that could impair safety.
Ten tyres had unsafe repairs, nine were over 10 years old and one was 23 years old.
The LGA is urging motorists buying second-hand tyres to check that they bear the required "part-worn" marking, which lets drivers know that the tyre has been checked and meets legal requirements.
There were 16 people killed and 908 road casualties - more than two a day - in reported accidents in the UK in 2015 where illegal, defective or under-inflated tyres were a contributory factor, according to Government figures.
Figures suggest that around 4.5 million part-worn tyres are being sold in the UK every year.
Simon Blackburn, chairman of the LGA's Safer and Stronger Communities Board, said: "The prevalence of dangerous used tyres for sale at some businesses is alarming and irresponsible traders have got questions to answer because they are putting lives at serious risk.
"Cheap part-worn tyres might be tempting to buy but if they don't have the correct legal markings, motorists risk buying illegal tyres which could contribute to a major accident.
"Motorists buying used tyres should go to a reputable trader and check they have 'part-worn' stamped on them as without this mark, they are unlikely to have been checked and the retailer is breaking the law.
"They should also look out for any cracks, tears, lumps and check the state of the tread before buying.
"It's also worth looking at how good a deal used tyres offer.
"New tyres are available to suit all budgets, provide a safer option and should last longer, meaning they may offer better value for money in the long term."