For your tyre to effectively grip the road, evacuate water and maintain control, your tyres need to have a safe amount of tread. If the grooves in the tyre design have almost disappeared, the tyre will simply not grip the road as well. This is particularly dangerous in wet conditions.
Plus, if you drive with tyres under the legal tread limit, you may be fined.
You should check the wear of your tyres regularly. If your tyres are approaching the legal limit or if you have any doubts, get them checked by a tyre professional. Or see below how to check it yourself.
1- Check the tread wear with a tread-depth gauge
Make sure that the hand brake is on and the car is in first gear (for manual gearboxes) or park (for automatics).
The legal minimum tread depth is 1.6 mm.
2- Check the tread wear indicators
Tyres have tread-wear indicators moulded into the base of the main grooves.
When the tread surface is worn to the same level as these indicators, the tyre is at the legal limit and should be replaced.
If you do not know or are confused with how to do this, take your car to a tyre shop and they will check for you and also show you what to look out for.