anewman:
Well it's a legal requirement that the driver ensures they are in legal condition. You can get a big fine and points PER TYRE that is illegal if pulled over by the police. Not checking won't be accepted as an excuse by an officer of the law!
Quite. Not to forget of course the safety factor - although the legal MINIMUM is 1.6mm, the ability of the tyre to shift water drops rapidly once below 3mm of tread. As the only part of the car in contact with the road I'm always shocked how blase people tend to be towards their tyres.