Rear marking plates may be fitted to the back of a caravan or trailer if the combined length of the towing vehicle and trailer is 7.5 metres in length or longer. However they are not compulsory.
Vehicles with an overall length of 7.5 metres or longer are permitted to display A ?DO NOT OVERTAKE TURNING VEHICLE? sign on the caravan/trailer. This can be either a separate sign located on the left handside or incorporated in the left hand side marking plate.