A surgical instrument has an end effector mounted on the end of an elongate shaft extending from a handle. The end-effector grasps, cuts, and seals and/or coagulates tissue, and one of the operations is controlled by a trigger mechanism. The trigger mechanism has an actuator, drive shaft and flanged component for transferring movement of the actuator to the drive shaft whose movement controls the end effector. The actuator has a collar portion arranged to receive and retain the component. The component is free to rotate within the collar and has a keyhole-shaped arrangement, with a wider upper portion, and narrower lower portion to provide a sliding fit to the component main body. The component can be inserted into the wider upper portion, and then the main body of the component lowered into the narrower lower portion, with the flange of the component helping the component to be retained therein axially.
