An electrosurgical apparatus comprising: an electrosurgical generator arranged to generate radiofrequency electromagnetic energy and a microwave electromagnetic energy; a bipolar electrosurgical instrument having a distal tip assembly for delivering RF electromagnetic energy and microwave electromagnetic energy into biological tissue; and a feed cable connected to deliver the RF electromagnetic energy and the microwave electromagnetic energy from the electrosurgical generator to the bipolar electrosurgical instrument, wherein the electrosurgical generator is arranged to detect a voltage and a current associated with the delivered RF electromagnetic energy, and wherein the generator is operable to: determine an impedance from the detected voltage and current; deliver the RF electromagnetic energy and the microwave electromagnetic energy in a composite waveform for promoting haemostasis in biological tissue, characterised in that the composite waveform comprises a first portion comprising primarily RF electromagnetic energy, and a second portion following the first portion, the second portion comprising primarily microwave electromagnetic energy, wherein the second portion further comprises a plurality of RF pulses, wherein the generator is arranged to: determine an impedance from the detected voltage and current during the first portion; and cause the composite waveform to transition from the first portion to the second portion when either: a duration of the first portion meets or exceeds a predetermined duration threshold, or the impedance determined during the first portion meets or exceeds a predetermined impedance threshold. an electrosurgical generator arranged to generate radiofrequency electromagnetic energy and a microwave electromagnetic energy; a bipolar electrosurgical instrument having a distal tip assembly for delivering RF electromagnetic energy and microwave electromagnetic energy into biological tissue; and a feed cable connected to deliver the RF electromagnetic energy and the microwave electromagnetic energy from the electrosurgical generator to the bipolar electrosurgical instrument, wherein the electrosurgical generator is arranged to detect a voltage and a current associated with the delivered RF electromagnetic energy, and wherein the generator is operable to: determine an impedance from the detected voltage and current; deliver the RF electromagnetic energy and the microwave electromagnetic energy in a composite waveform for promoting haemostasis in biological tissue, characterised in that the composite waveform comprises a first portion comprising primarily RF electromagnetic energy, and a second portion following the first portion, the second portion comprising primarily microwave electromagnetic energy, determine an impedance from the detected voltage and current; deliver the RF electromagnetic energy and the microwave electromagnetic energy in a composite waveform for promoting haemostasis in biological tissue, characterised in that the composite waveform comprises a first portion comprising primarily RF electromagnetic energy, and a second portion following the first portion, the second portion comprising primarily microwave electromagnetic energy, a first portion comprising primarily RF electromagnetic energy, and a second portion following the first portion, the second portion comprising primarily microwave electromagnetic energy, wherein the second portion further comprises a plurality of RF pulses, wherein the generator is arranged to: determine an impedance from the detected voltage and current during the first portion; and cause the composite waveform to transition from the first portion to the second portion when either: a duration of the first portion meets or exceeds a predetermined duration threshold, or the impedance determined during the first portion meets or exceeds a predetermined impedance threshold. determine an impedance from the detected voltage and current during the first portion; and cause the composite waveform to transition from the first portion to the second portion when either: a duration of the first portion meets or exceeds a predetermined duration threshold, or the impedance determined during the first portion meets or exceeds a predetermined impedance threshold. a duration of the first portion meets or exceeds a predetermined duration threshold, or the impedance determined during the first portion meets or exceeds a predetermined impedance threshold.