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 contained within the handle. In some embodiments, the end effector includes a blade assembly, the trigger mechanism being arranged to drive the blade assembly longitudinally within the elongate shaft in order to cut tissue. Specifically, the trigger mechanism is formed of a three pivot slider-crank mechanism, wherein one of the pivot points comprises a component to which the proximal end of the blade assembly is connected. In this respect, the proximal end of the blade assembly has a distinctive profile corresponding to the internal profile of the component such that the blade can be easily connected to the component without the need for any further features and subsequently retained therein. Such a configuration therefore provides a secure arrangement that simplifies the assembly of the instrument. <；Figure 21>；
