The majority of drivers are unaware of the legal minimum tyre tread depth for their vehicle, meaning millions of motorists could be putting lives at risk.

The AA is now warning fleet managers of the risks of breaching health and safety law, should their drivers travel with sub-standard tyres.

If employers fail in their duty of care to their drivers they could face imprisonment or a £20,000 fine, while drivers could rack up three penalty points and a £1,000 fine for each illegal tyre.

Paul Holmes, head of risk management at AA Business Services, said: “Due to the amount of mileage covered by company car drivers, checks between service intervals are essential, especially in the winter.”

Two thirds of drivers (68%) do not know that the minimum tread depth for cars and vans is 1.6mm, according to a survey by motoring charity Brake and recovery service Green Flag.

Now the road safety charity is urging drivers to check tread depth, tyre pressure and look for any other damage such as bulges and tears weekly and again before every long journey.

Jools Townsend, head of education at Brake, said: “Many drivers are unaware of the deterioration that happens to their vehicle over the course of a year.”