UK Tyre Laws
The main reason a tyre has tread is to disperse water efficiently. The less tread you have, the more likely you are to skid or aquaplane on wet roads and lose steering control.
It is illegal to run a tyre with less than 1.6mm of tread round the entire outer circumference of the tyre. Tyre manufacturers build a number of tread wear indicator bars into the tread area of their tyres which become visible at 1.6mm. These serve as a useful visual reminder to change your tyres.
However, wet weather braking and cornering efficiency reduce considerably as the tyre wears down and dustcap strongly advises that you change your tyres before you reach the legal limit.
The penalty for driving with illegal tyres on your car is very severe. There is a compulsory driving licence endorsement of three penalty points and a fine of up to £2,500 for each illegal tyre.