I don't think the rules below count if on private land ie Caravan Site, but you are not allowed to have audible reversing sounds on a public highway unless you are a good vehicle over 2000kg.
(3) No person shall sound, or cause or permit to be sounded, on a road any reversing alarm fitted to a vehicle—
(a)unless the vehicle is a goods vehicle which has a maximum gross weight not less than 2000 kg, a bus, engineering plant, or a works truck; or
(b.) if the sound of the alarm is likely to be confused with a sound emitted in the operation of a pedestrian crossing established, or having effect as if established, under Part III of the 1984 Act.