An electrosurgical instrument having an elongate probe comprising: a coaxial transmission line for conveying radiofrequency (RF) and/or microwave electromagnetic (EM) radiation; a probe tip at a distal end of the coaxial transmission line for receiving the RF and/or microwave energy; a liquid channel for conveying liquid to the probe tip; and a gas channel for conveying gas to the probe tip; wherein the coaxial transmission line includes an inner conductor, an outer conductor, and a first dielectric material separating the inner conductor from the outer conductor, wherein the probe tip comprises a rigid second dielectric material having a probe tip channel running therethrough, the probe tip channel being in fluid communication with the liquid channel and terminating in an aperture at its distal end, wherein the probe tip includes a first electrode connected to the inner conductor of the coaxial transmission line and a second electrode connected to the outer conductor of the coaxial transmission line, the first electrode and the second electrode each comprising a conductive structure on an outer surface of the probe tip and being selectively operable in a plasma generating mode or a non-ionising radiation mode, wherein, in the plasma generating mode, the first electrode and second electrode are arranged around a flow path of gas from the gas channel over the outer surface of the probe tip, whereby the RF and/or microwave EM energy from the coaxial transmission line is deliverable to strike and sustain a thermal or non-thermal plasma in gas delivered along the flow path, and wherein, in the non-ionising radiation mode, at least one of the first electrode and the second electrode is configured as a radiating antenna structure for emitting a microwave EM field outwardly from the probe tip. a coaxial transmission line for conveying radiofrequency (RF) and/or microwave electromagnetic (EM) radiation; a probe tip at a distal end of the coaxial transmission line for receiving the RF and/or microwave energy; a liquid channel for conveying liquid to the probe tip; and a gas channel for conveying gas to the probe tip; wherein the coaxial transmission line includes an inner conductor, an outer conductor, and a first dielectric material separating the inner conductor from the outer conductor, wherein the probe tip comprises a rigid second dielectric material having a probe tip channel running therethrough, the probe tip channel being in fluid communication with the liquid channel and terminating in an aperture at its distal end, wherein the probe tip includes a first electrode connected to the inner conductor of the coaxial transmission line and a second electrode connected to the outer conductor of the coaxial transmission line, the first electrode and the second electrode each comprising a conductive structure on an outer surface of the probe tip and being selectively operable in a plasma generating mode or a non-ionising radiation mode, wherein, in the plasma generating mode, the first electrode and second electrode are arranged around a flow path of gas from the gas channel over the outer surface of the probe tip, whereby the RF and/or microwave EM energy from the coaxial transmission line is deliverable to strike and sustain a thermal or non-thermal plasma in gas delivered along the flow path, and wherein, in the non-ionising radiation mode, at least one of the first electrode and the second electrode is configured as a radiating antenna structure for emitting a microwave EM field outwardly from the probe tip. <EOS>