An electrosurgical instrument comprising: an elongate probe having: a coaxial transmission line for conveying microwave electromagnetic energy, a probe tip connected at the distal end of the coaxial transmission line for receiving the microwave energy, and a liquid channel located inside the coaxial transmission line for conveying liquid through the elongate probe to the probe tip, wherein the coaxial transmission line comprises: a hollow inner conductor, an outer conductor, a first dielectric material separating the inner conductor from the outer conductor, and a hollow second dielectric material on an inner surface of the hollow inner conductor, the liquid channel located inside the hollow second dielectric material; wherein the probe tip has a probe tip channel running therethrough, the probe tip channel terminating in an aperture at its distal end, wherein the probe tip includes a conductive element coupled to receive microwave energy from the coaxial transmission line, the conductive element forming a radiating antenna structure for emitting a microwave EM field outwardly from the probe tip, and wherein the instrument further comprises a hollow needle located inside the liquid channel, wherein a first end of the needle is in fluid communication with the liquid channel and a second end of the needle is arranged to deliver liquid from the liquid channel through the aperture of the probe tip channel to a target area. an elongate probe having: a coaxial transmission line for conveying microwave electromagnetic energy, a probe tip connected at the distal end of the coaxial transmission line for receiving the microwave energy, and a liquid channel located inside the coaxial transmission line for conveying liquid through the elongate probe to the probe tip, a coaxial transmission line for conveying microwave electromagnetic energy, a probe tip connected at the distal end of the coaxial transmission line for receiving the microwave energy, and a liquid channel located inside the coaxial transmission line for conveying liquid through the elongate probe to the probe tip, wherein the coaxial transmission line comprises: a hollow inner conductor, an outer conductor, a first dielectric material separating the inner conductor from the outer conductor, and a hollow second dielectric material on an inner surface of the hollow inner conductor, the liquid channel located inside the hollow second dielectric material; a hollow inner conductor, an outer conductor, a first dielectric material separating the inner conductor from the outer conductor, and a hollow second dielectric material on an inner surface of the hollow inner conductor, the liquid channel located inside the hollow second dielectric material; wherein the probe tip has a probe tip channel running therethrough, the probe tip channel terminating in an aperture at its distal end, wherein the probe tip includes a conductive element coupled to receive microwave energy from the coaxial transmission line, the conductive element forming a radiating antenna structure for emitting a microwave EM field outwardly from the probe tip, and wherein the instrument further comprises a hollow needle located inside the liquid channel, wherein a first end of the needle is in fluid communication with the liquid channel and a second end of the needle is arranged to deliver liquid from the liquid channel through the aperture of the probe tip channel to a target area.