Your tyres must comply with the legal minimum of [1.6 mm] tread depth. The minimum safety recommendation for summer tyres is 3 mm and 4 mm for winter tyres.
Worn tyres could mean that you need up to 70% more braking distance to slow down on a wet road.
Worn tyres increase road noise, affect your vehicle's handling making manoeuvres unpredictable.
Low tyre pressures will cause your car to use more fuel. Filling your tyres 0.1 to 0.3 bar over the recommended level helps reduce road resistance. However, you should never exceed the maximum pressure recommended for driving with a full load.
On wet roads worn tyres can result in your car skidding, becoming difficult to handle or loss of control.