An electrosurgery system includes an electrosurgical generator (
) coupled to or part of an electrosurgical instrument, the generator being operable to generate electrosurgical power in low frequency (typically at 1 MHz) and high frequency bands (typically at 2.45 GHz) either simultaneously or individually the generator includes a load-responsive control circuit which, in one mode, causes power to be generated predominantly at 1 MHz when the load impedance is high and predominantly at 2.45 MHz when it is low. This allows automatic switching between cutting and coagulation operation. In one embodiment, the instrument includes a gas plasma generator operating such that an ionizable gas is energized in a gas supply passage by the 2.45 GHz component to form a plasma stream which acts as a conductor for delivering the 1 MHz component to a tissue treatment outlet of the passage. (FIG.