Embodiments of the present invention provide an improved surgical instrument having an end effector mounted on the end of an elongate shaft extending from a handle. The end-effector is capable of several different operations, including grasping, cutting, and sealing and/or coagulating tissue, and one of the operations is controlled by a trigger mechanism as described herein. The trigger mechanism comprises an actuator, a drive shaft and a flanged component for transferring movement of the actuator to the drive shaft, wherein movement of the drive shaft controls the end effector. The trigger mechanism is configured so as to allow easy assembly, as well as maximum control of the end effector. Specifically, the actuator is provided with a collar portion arranged to receive and then retain the component, wherein the component is free to rotate within the collar. In this regard, the collar portion has a keyhole-shaped arrangement, with a wider upper portion, and narrower lower portion, the narrower lower portion being of a width to provide a close sliding fit to the main body of the component. In order to assemble the component within the collar 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. Such an arrangement provides ease of assembly, whilst allowing rotation of the end effector and maintaining the responsiveness of the end effector to the trigger mechanism. <；Figure 8a>；
