A vehicle suspension system control unit (40) is arranged to determine from a lateral accelerometer (42) and vehicle speed sensor (44) when the vehicle is executing a series of opposite turns in a slalom type manner which are likely to cause a build-up of body roll. In this situation the roll control system is modified from a regime in which some body roll is allowed, to a regime in which body roll is substantially prevented thereby to prevent the build up of body roll during slalom type manoeuvres.