You must NOT sound your horn

Explanation: Vehicles can be noisy. Every effort must be made to prevent excessive noise, especially in built-up areas at night. Don't
- rev the engine,
- sound the horn unnecessarily. It is illegal to sound your horn in a built-up area between 11.30 pm and 7 am, except when another vehicle poses a danger.

Category: Safety and Your Vehicle

References: The Official DVSA Guide to Driving: Section 3, Highway Code: Rule 112