Regulation 103 Leaving trailers at rest

A person in charge of a motor vehicle, or trailer drawn by it, shall not cause or permit such trailer to stand on a road when detached from the drawing vehicle unless one at least of the wheels of the trailer is (or, in the case of a track-laying trailer, its tracks are) prevented from revolving by the setting of the parking brake or the use of a chain, chock or other efficient device.