An electrosurgical resection instrument (200, 282, 402) for applying to biological tissue radiofrequency electromagnetic energy having a first frequency and microwave EM energy having a second frequency higher than the first frequency, the instrument comprising: an instrument tip (202, 283, 300) comprising a body made of a first dielectric material separating a first conductive element from a second conductive element; a coaxial feed cable (224, 406) comprising an inner conductor, an outer conductor coaxial with the inner conductor, and a second dielectric material separating the outer and inner conductors, the coaxial feed cable being for conveying, simultaneously or separately, an RF signal having the first frequency and a microwave signal having the second frequency; and a fluid feed conduit for delivering fluid to the instrument tip; wherein the inner conductor is electrically connected to the first conductive element and the outer conductor is electrically connected to the second conductive element to enable the instrument tip to receive the RF signal and the microwave signal, and wherein the first and second conductive elements are arranged to act: as active and return electrodes to convey RF EM radiation corresponding to the RF signal, and as an antenna to radiate microwave EM radiation corresponding to the microwave signal, characterised in that: the fluid feed conduit is arranged to deliver liquid to the instrument tip, the fluid feed conduit having an outlet at the distal end of the instrument tip for introducing the liquid into the biological tissue. an instrument tip (202, 283, 300) comprising a body made of a first dielectric material separating a first conductive element from a second conductive element; a coaxial feed cable (224, 406) comprising an inner conductor, an outer conductor coaxial with the inner conductor, and a second dielectric material separating the outer and inner conductors, the coaxial feed cable being for conveying, simultaneously or separately, an RF signal having the first frequency and a microwave signal having the second frequency; and a fluid feed conduit for delivering fluid to the instrument tip; wherein the inner conductor is electrically connected to the first conductive element and the outer conductor is electrically connected to the second conductive element to enable the instrument tip to receive the RF signal and the microwave signal, and wherein the first and second conductive elements are arranged to act: as active and return electrodes to convey RF EM radiation corresponding to the RF signal, and as an antenna to radiate microwave EM radiation corresponding to the microwave signal, as active and return electrodes to convey RF EM radiation corresponding to the RF signal, and as an antenna to radiate microwave EM radiation corresponding to the microwave signal, characterised in that: the fluid feed conduit is arranged to deliver liquid to the instrument tip, the fluid feed conduit having an outlet at the distal end of the instrument tip for introducing the liquid into the biological tissue. the fluid feed conduit is arranged to deliver liquid to the instrument tip, the fluid feed conduit having an outlet at the distal end of the instrument tip for introducing the liquid into the biological tissue.