An actuator, comprises a housing, a first prime mover for producing rotary motion, a first gearbox arranged to convert in use the rotary motion from the first prime mover into rotary motion having higher torque and lower speed. The first gearbox comprises a casing mounted for rotation relative to the housing of the actuator and a second gearbox arranged to convert rotary motion of the casing of the first gearbox into rotary motion having lower torque and higher speed. A brake is arranged to act on the rotary motion having lower torque and higher speed from the second gearbox. In use when the first gearbox is not jammed, the brake may be applied to resist relative rotation between the casing of the first gearbox and the housing of the actuator. When the first gearbox is jammed, the brake may be released thereby allowing the casing of the first gearbox to rotate relative to the housing of the actuator. The actuator may thereby be jam-tolerant. A second motor may also be provided.