The actuator (10) comprises a barrel (16) and a plunger (22) received within the barrel. A clutch mechanism (54) is operable between the plunger and the barrel. In the engaged condition of the clutch, the plunger is advanced by rotation relative to the barrel. An axial load on the plunger disengages the clutch mechanism, allowing the plunger to be advanced axially whilst rotating the driven member (60). Two-handed or one-handed operation is therefore possible. A freely rotatable collar (27) on the plunger allows the plunger to be returned to its retracted position with a linear rearward movement whilst allowing rotation of the plunger.
