An electrosurgical instrument comprising: an elongate probe comprising a coaxial cable for conveying radiofrequency and/or microwave frequency electromagnetic energy, and a probe tip connected at the distal end of the coaxial cable for receiving the RF and/or microwave energy; and a gas passage for conveying gas through the elongate probe to the probe tip, wherein the coaxial cable comprises an inner conductor, an outer conductor and a dielectric material separating the inner conductor from the outer conductor, wherein the probe tip comprising a first electrode connected to the inner conductor of the coaxial cable and a second electrode connected to the outer conductor of the coaxial cable, characterised in that: the first electrode and second electrode are movable relative to each other between: a first configuration in which they are arranged to produce an electric field from the received RF and/or microwave frequency EM energy across a flow path of gas received from the gas passage to produce a thermal or non-thermal plasma, and a second configuration in which the first electrode extends distally beyond the second electrode to form a radiating structure for emitting a microwave EM field outwardly from the probe tip. an elongate probe comprising a coaxial cable for conveying radiofrequency and/or microwave frequency electromagnetic energy, and a probe tip connected at the distal end of the coaxial cable for receiving the RF and/or microwave energy; and a gas passage for conveying gas through the elongate probe to the probe tip, wherein the coaxial cable comprises an inner conductor, an outer conductor and a dielectric material separating the inner conductor from the outer conductor, wherein the probe tip comprising a first electrode connected to the inner conductor of the coaxial cable and a second electrode connected to the outer conductor of the coaxial cable, characterised in that: the first electrode and second electrode are movable relative to each other between: a first configuration in which they are arranged to produce an electric field from the received RF and/or microwave frequency EM energy across a flow path of gas received from the gas passage to produce a thermal or non-thermal plasma, and a second configuration in which the first electrode extends distally beyond the second electrode to form a radiating structure for emitting a microwave EM field outwardly from the probe tip. the first electrode and second electrode are movable relative to each other between: a first configuration in which they are arranged to produce an electric field from the received RF and/or microwave frequency EM energy across a flow path of gas received from the gas passage to produce a thermal or non-thermal plasma, and a second configuration in which the first electrode extends distally beyond the second electrode to form a radiating structure for emitting a microwave EM field outwardly from the probe tip. a first configuration in which they are arranged to produce an electric field from the received RF and/or microwave frequency EM energy across a flow path of gas received from the gas passage to produce a thermal or non-thermal plasma, and a second configuration in which the first electrode extends distally beyond the second electrode to form a radiating structure for emitting a microwave EM field outwardly from the probe tip.