A method of operating an electrosurgical apparatus for coagulating tissue comprises inserting the electrosurgical instrument (1) into an endoscope (7), and activating a source to supply ionisable gas to the electrosurgical instrument (1) at a flow rate of less than a predetermined threshold flow rate while the electrosurgical instrument is being inserted into the endoscope (7). Once the electrosurgical instrument has been fully inserted into the endoscope (7), the source is activated to supply ionisable gas to the electrosurgical instrument at a flow rate of greater than the predetermined threshold flow rate. Finally, high frequency energy is supplied from an electrosurgical generator (5) to the electrosurgical instrument (1), in order to ionise the ionisable gas flowing to the electrosurgical instrument.
