Highway Code Rule 286

If you are involved in a collision which causes damage or injury to any other person, vehicle, animal or property, you MUST

stop
give your own and the vehicle owner’s name and address, and the registration number of the vehicle, to anyone having reasonable grounds for requiring them
if you do not give your name and address at the time of the collision, report it to the police as soon as reasonably practicable, and in any case within 24 hours.

Section: Breakdowns and incidents (rules 274 to 287)
Subsection: Documentation (rules 286 to 287)