A bipolar electrosurgical instrument includes first and second shafts each having a jaw member extending from its distal end. Each jaw member is adapted to connect to a source of electrosurgical energy such that the jaw members are capable of selectively conducting energy through tissue held therebetween. A knife channel is configured to reciprocate a cutting mechanism therealong. An actuator selectively advances the cutting mechanism. A switch is disposed on the first shaft and is configured to be depressed between a first position and at least one subsequent position upon biasing engagement with a mechanical interface disposed on the second shaft. The first position of the switch relays information to the user corresponding to a desired pressure on tissue and the at least one subsequent position is configured to activate the source of electrosurgical energy to supply electrosurgical energy to the jaw members. The invention in particular relates to a vessel sealing instrument.