Abstract: The invention provides a castor wheel assembly 10 in which the swivel or castor axis 16 is locked when the wheel 11 is in the straight ahead position, but unlocked in any other position of motion, locking being caused by forward rotation of the wheel and released by backward rotation both without any braking action on the wheel. A supermarket trolley or similar vehicle equipped with a pair of such castors at the front end and conventional castors at the rear can be steered under normal circumstances by the rear castors but readily adapted to four wheel steering in confined spaced by slight reverse motion to unlock the front wheels' castor action.