Leaving trailers at restE+W+S
89. No person in charge of a motor vehicle, or trailer drawn thereby, shall 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 [F1a parking brake] or the use of a chain, chock or other efficient device.