Linear actuator for selectively actuating an actuatable device, the linear actuator comprising: a support; a piston mounted on the support for movement generally along an actuation axis through a range of motion including an actuating position and a non-actuating position, the piston being movable in a first axial direction extending from the actuating position toward the non-actuating position and a second axial direction opposite the first axial direction, the piston including at least one retainer element and being configured to be mechanically connected to a movable input member of the actuatable device to position the input member at an actuated position; an automatic driver configured to selectively drive movement of the piston to the actuating position and the non-actuating position using power supplied by a power source; the linear actuator being characterised in that it further comprises a manual driver configured to selectively drive movement of the piston to the actuating position and the non-actuating position using a manual force, the manual driver comprising: a manual input member rotatably mounted on the support for selective rotation about the axis with respect to the support; and a linking member threadably engaged with the manual input member for movement relative to the manual input member along the actuation axis when the manual input member is rotated relative to the linking member about the axis, the linking member including at least one retainer formation configured for interlocking engagement with the at least one retainer element of the output assembly, the interlocking engagement between the retainer formation and the retainer element being operative to: inhibit relative rotation between the piston and the linking member about the actuation axis; inhibit movement of the piston relative to the linking member along the axis in one of the first and second axial directions; and permit movement of the piston relative to the linking member along the axis in the other of the first and second axial directions. a support; a piston mounted on the support for movement generally along an actuation axis through a range of motion including an actuating position and a non-actuating position, the piston being movable in a first axial direction extending from the actuating position toward the non-actuating position and a second axial direction opposite the first axial direction, the piston including at least one retainer element and being configured to be mechanically connected to a movable input member of the actuatable device to position the input member at an actuated position; an automatic driver configured to selectively drive movement of the piston to the actuating position and the non-actuating position using power supplied by a power source; the linear actuator being characterised in that it further comprises a manual driver configured to selectively drive movement of the piston to the actuating position and the non-actuating position using a manual force, the manual driver comprising: a manual input member rotatably mounted on the support for selective rotation about the axis with respect to the support; and a linking member threadably engaged with the manual input member for movement relative to the manual input member along the actuation axis when the manual input member is rotated relative to the linking member about the axis, the linking member including at least one retainer formation configured for interlocking engagement with the at least one retainer element of the output assembly, a manual input member rotatably mounted on the support for selective rotation about the axis with respect to the support; and a linking member threadably engaged with the manual input member for movement relative to the manual input member along the actuation axis when the manual input member is rotated relative to the linking member about the axis, the linking member including at least one retainer formation configured for interlocking engagement with the at least one retainer element of the output assembly, the interlocking engagement between the retainer formation and the retainer element being operative to: inhibit relative rotation between the piston and the linking member about the actuation axis; inhibit movement of the piston relative to the linking member along the axis in one of the first and second axial directions; and permit movement of the piston relative to the linking member along the axis in the other of the first and second axial directions. inhibit relative rotation between the piston and the linking member about the actuation axis; inhibit movement of the piston relative to the linking member along the axis in one of the first and second axial directions; and permit movement of the piston relative to the linking member along the axis in the other of the first and second axial directions.