People are much safer travelling in a car if they’re wearing seatbelts. Wearing seatbelts is the law, and if your car has them - and most cars do - you and your passengers must use them.
Always ask your passengers to put on their seatbelts. Explain that it’s safer, and that you could lose your licence and be fined if they don’t.
Remember that if the police stop you, you will be fined if your passengers are not wearing appropriate seatbelts or child restraints.