If you're involved in a minor collision, no injury is caused to anyone involved in the collision, and all parties have exchanged details, then there is no requirement to report this to the police.
If, as a driver of a vehicle (including car, motorcycle or bus), you are involved in a in accident in which;
- A person, other than yourself, is injured
- Damage has been caused to another vehicle or to someone else’s property – including street lamps, signs, bollards etc
- An animal, other than one in your own vehicle/trailer, has been killed or injured
...then you must stop and provide your details. If you do not, then you must report it to the police on 101.