The invention relates to an electrosurgical device and especially to an improved surgical device.A surgical instrument having an end effector mounted on the end of an elongate shaft extending from a handle. The end-effector is capable of 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. Specifically, the trigger mechanism is formed of a three pivot slider-crank mechanism, wherein one of the pivot points includes 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.