For members outside the UK: In the UK, all cars and motorbikes over three years old have to pass an annual roadworthiness test called an MOT (there's a similar equivalent in Ireland called the NCT). According to the current inspection manual, you can fail this test if: Basically, if you do fit a musical horn, unless your car dates from before 1973, make sure you keep the original horn for road use. During my Googling, I read an account of a driver who used to like sounding his Dixie horn when he was overtaking other cars. One day he made the mistake of doing this while overtaking an unmarked police can, and was prosecuted. PS. According to section 2. c. (above), "hells bells" are also illegal .