UK law requires that your vehicle is fitted with the correct type and size of tyre for the vehicle type you are driving and for the purpose it is being used. This means fitting the right tyres and for safety ensuring that they are inflated to the manufacturer's recommended pressure.
The legal limit for minimum depth of the tread on your tyres is 1.6 millimetres, across the central ¾ of the tread around the complete circumference of the tyre.
For safety reasons it is recommended that you replace your tyres before the legal limit is reached. Many vehicle manufacturers recommend replacing at 3 millimetres. To see the impact on braking distance of different tyre tread depths, At 1.6 millimetres in wet weather it takes an extra car length (8 metres) to stop at 50 mph than if your tread was 3 millimetres.
A regular check of your tyres can help you to avoid 3 penalty points and £2,500 in fines (per tyre) for having tyres worn beyond the legal minimum limit on your vehicle.