An electrosurgical instrument for delivering electromagnetic energy to biological tissue, the instrument comprising: a distal end assembly comprising: an active tip comprising a planar body made of a first dielectric material separating a first conductive element on a first surface thereof from a second conductive element on a second surface thereof, the second surface facing in the opposite direction to the first surface; an electrically conductive protective hull mounted on an underside of the active tip, the protective hull having a smoothly contoured convex undersurface facing away from the planar body; and a coaxial feed cable comprising an inner conductor, an outer conductor coaxial with the inner conductor and a second dielectric material separating the inner and outer conductors, the coaxial feed cable being for conveying RF EM energy or microwave EM energy, wherein the inner conductor is electrically connected to the first conductive element and the outer conductor is electrically connected to the second conductive element via the protective hull to enable the instrument tip to receive the RF and/or the microwave signal, wherein the first and second conductive elements are arranged to emit the RF EM energy or the microwave EM energy from the coaxial cable at a distal side portion of the planar body, wherein the distal end assembly comprises a flexible shaft connected to a proximal end of the protective hull, the shaft defining a lumen for conveying the coaxial cable, wherein the flexible shaft comprises: a proximal cannula tube having braids formed therein to assist in the transfer of torque from its proximal end to the distal end assembly; and a distal unbraided tubular portion bonded to a distal end of the cannula tube, and wherein the flexible shaft comprises a support tube mounted at a junction between the proximal cannula tube and the unbraided tubular portion. a distal end assembly comprising: an active tip comprising a planar body made of a first dielectric material separating a first conductive element on a first surface thereof from a second conductive element on a second surface thereof, the second surface facing in the opposite direction to the first surface; an electrically conductive protective hull mounted on an underside of the active tip, the protective hull having a smoothly contoured convex undersurface facing away from the planar body; and an active tip comprising a planar body made of a first dielectric material separating a first conductive element on a first surface thereof from a second conductive element on a second surface thereof, the second surface facing in the opposite direction to the first surface; an electrically conductive protective hull mounted on an underside of the active tip, the protective hull having a smoothly contoured convex undersurface facing away from the planar body; and a coaxial feed cable comprising an inner conductor, an outer conductor coaxial with the inner conductor and a second dielectric material separating the inner and outer conductors, the coaxial feed cable being for conveying RF EM energy or microwave EM energy, wherein the inner conductor is electrically connected to the first conductive element and the outer conductor is electrically connected to the second conductive element via the protective hull to enable the instrument tip to receive the RF and/or the microwave signal, wherein the first and second conductive elements are arranged to emit the RF EM energy or the microwave EM energy from the coaxial cable at a distal side portion of the planar body, wherein the distal end assembly comprises a flexible shaft connected to a proximal end of the protective hull, the shaft defining a lumen for conveying the coaxial cable, wherein the flexible shaft comprises: a proximal cannula tube having braids formed therein to assist in the transfer of torque from its proximal end to the distal end assembly; and a distal unbraided tubular portion bonded to a distal end of the cannula tube, and wherein the flexible shaft comprises a support tube mounted at a junction between the proximal cannula tube and the unbraided tubular portion. a proximal cannula tube having braids formed therein to assist in the transfer of torque from its proximal end to the distal end assembly; and a distal unbraided tubular portion bonded to a distal end of the cannula tube, and wherein the flexible shaft comprises a support tube mounted at a junction between the proximal cannula tube and the unbraided tubular portion.