Only found this out the other day, but you're not allowed to sound your horn unless you're in danger 
The coppers pulled me over for honking at a guy in front of me that was blocking the traffic, and he had loads of room to do his right turn.
They told me they could have fined me - the world has gone mad!!! 
....Well yes, the world has gone mad! But what I understand is as follows:
- Use of the horn while stationary, at night in a residential area, or in an aggressive manner is against the Highway Code.
It says motorists should beep their horns only "
while your vehicle is moving and you need to warn other road users of your presence". < Which is essentially what I wrote in my review.
- The horn should not be used while stationary on the road or when driving in a built-up area between 11:30pm and 7:00am "
except when another vehicle poses a danger".
Although breaching the code is not a criminal offence, many of its guidelines refer to legal requirements, and the instructions on using the horn is one of them.
- Improper use of the horn is contrary to regulation 99 (1) of the Road Vehicles (Construction and Use) Regulations 1986, section 42 of the Road Traffic Act 1988 and Schedule 2 to the Road Traffic Offenders Act 1988'.
- For what he judges to be improper use, a Police Officer can issue a motorist caught breaking the law with a £30 fixed penalty notice.
Drivers can challenge the decision at court, but if magistrates agree with the police they can increase the fine to up to £1,000 < That's not the practice of fair justice in my opinion.
Perhaps the Policeman (more than one?) took the view that your "honking at a guy in front of you" was aggressive and also because your car was stationary. I'm not trying to suggest that you were in the wrong - Personally I think use of the horn (for everyone else except myself) is a matter of common sense and it's good that the Police didn't issue you with a penalty.
Did they explain the details of the law which you appear to have broken?
