Road users warned about the millimetre difference making cars illegal

The study of nearly 500 cars at 100 locations found eight per cent were also offered for sale with treads below 3mm, which would receive a warning during testing.

One £8,000 vehicle in the sample was being offered for sale from a dealership with visibly damaged tyres with 1.55mm of tread and a 10-month MOT. While a dealership for a major brand was offering a £15,000 car with a 12 month MOT and tyres with just 1.6mm of tread - both cars were available for a test drive.

Currently, cars can be legally sold second-hand with a 12 month MOT and 1.6mm of tread - the road-legal limit - when just 0.01mm of wear would render them illegal. This would take approximately 33 miles - meaning the vehicle could be illegal by the time the new owner gets their vehicle back home. But four vehicles out of the 481 in the study were found to have tyres at 1.6mm or less, rendering them illegal – or micrometres away from illegal.

Despite many being sold at legal or advisory depths, the average car uses 2mm of wear per year, taking it close to or beyond the legal limits after they’re sold.

The study was commissioned by Halfords overseen by Professor Peter Wells, Director of the Centre for Automotive Research at Cardiff University, ahead of Tyre Safety Month.

Halfords Garages MD, Adam Pay, said: “The current rules for tread depth on cars sold do not put motorists’ safety first. Most motorists do not check tyres between MOTs and expect a car they have bought will be safe until its next MOT. The fact it is legal to sell a car with a 12 month MOT that, in a matter of miles or days will be illegal, at best lacks common sense and at worse could cost lives. The law needs an urgent rethink.”

It comes after research of 2,000 motorists, also commissioned by Halfords, found half who purchased a second-hand car in the past year have already had to change at least one tyre. And if they were to buy a second-hand vehicle with less than 3mm of tread, 40 per cent would feel ‘let down’ and 35 per cent as if they were being ‘put in danger’.

Professor Peter Wells, called the findings extremely worrying and ‘an accident waiting to happen’.

He estimated that based on the figures, around 1.2m cars are being sold with potentially dangerous tyres each year, while over 75,000 are likely sold with completely illegal ones.

He said: “Tyres are one of, if not the most safety-critical aspect of a vehicle. Once they approach 3mm, their braking and roadholding ability has already begun deteriorating noticeably and it only gets worse from there. The difference in stopping distance between new tyres and ones with 1.6mm of tread is 75 meters if travelling at 70mph in wet conditions.

“That’s the difference between stopping in time, or crashing at 46mph - there is a question of whether 1.6mm should be road-legal at all. I would propose that imposing a legal limit of 3.6mm, or even 4mm, would be sensible.”