Trailer suspension system

A control system for a trailer, the trailer comprising a trailer deck and a suspension system which is controllable to adjust the height of the trailer deck above the surface on which the trailer rests, the control system comprising: a processor which is operable to control the suspension system; and a determining arrangement to determine automatically the height of a surface of a loading bay in proximity to the trailer, either relative to the surface on which the trailer rests or relative to a part of the trailer, wherein the processor its operable to adjust the height of the trailer deck, in response to information from the determining arrangement, to match substantially that of the surface of the loading bay.