In the hydraulically assisted steering system disclosed herein, a hydraulic pump for powering a steering servo is in turn driven either from the vehicle's engine, through an electrically controlled clutch, or by an electric motor which can drive the pump independently of the vehicle's engine. A signal is provided which varies as a function of vehicle's speed and disengagement of the clutch is enabled for vehicle speeds above a predetermable threshold, thereby to reduce energy consumption. The clutch is engaged, independently of vehicle speed, under high load, e.g. emergency situations.