Motorists are being cautioned about a lesser-known Highway Code rule over the use of their car horn, which could result in them receiving a (PCN).

Rule 112 of the , which outlines how to properly use your horn, states: "Use only while your vehicle is moving and you need to warn other road users of your presence." It goes on to say: "You MUST NOT use your horn while stationary on the road".

This means that drivers who honk their horn while stuck in traffic or when they park up to signal their arrival are breaking the rules. This could apply even if you sound the horn on your own driveway.

The Highway Code also says you should "never sound your horn aggressively" and prohibits its use "when driving in a built-up area between the hours of 11.30 pm and 7.00 am". However, there is an exception to these rules, which allows you to use your horn "when another road user poses a danger."

Therefore, even if your car is stationary or it's early morning, you can still honk your horn for safety reasons such as warning others of a hazard.

PCNs, or Penalty Charge Notices, are not just for parking offences. They can also be issued for traffic violations such as improper use of your car horn.

The cost of a PCN varies depending on the severity of the offence and the area in which it was committed. For instance, in London, a PCN can be issued for "minor moving traffic contraventions" of £130, with a 50% discount if paid within 14 days. However, ignoring a PCN could result in a court case and potentially push your bill into the thousands.

Motorists are also advised to ensure their horn is functioning properly before taking their vehicle in for an MOT. As per the , the audible warning (horn) "must be loud enough to be heard by other road users". A non-working horn could lead to a major fault on an MOT, resulting in a fail.

There are even specific guidelines about what your horn must sound like to avoid confusion with emergency vehicles. Gongs, bells, and sirens are all prohibited - unless you own a classic car from before 1906 - and the sound must be continuous and uniform. The sound must also not be "harsh or grating", ruling out novelty horns.