An electrosurgical instrument for applying radiofrequency energy and/or microwave frequency energy to biological tissue, the instrument comprising: a distal part comprising an instrument tip for applying radiofrequency energy and/or microwave frequency energy to biological tissue, wherein the instrument tip comprises a first conductive element and a second conductive element; a coaxial feed cable comprising an inner conductor, a tubular outer conductor coaxial with the inner conductor, and a dielectric material separating the inner and outer conductors, the coaxial feed cable being for conveying radiofrequency energy and/or microwave frequency energy to the distal part; wherein: the inner conductor is electrically connected to the first conductive element and the outer conductor is electrically connected to the second conductive element through a rotatable connection between the distal part and the coaxial feed cable that allows rotation of the distal part relative to the coaxial feed cable about a central axis of the distal part; the instrument comprises an actuator for rotating the distal part in a first rotational direction relative to the coaxial feed cable; characterized in that the rotatable connection comprises a flexible transmission line, the flexible transmission line having a first conductive path electrically connecting the inner conductor to the first conductive element and a second conductive path electrically connecting the outer conductor to the second conductive element. a distal part comprising an instrument tip for applying radiofrequency energy and/or microwave frequency energy to biological tissue, wherein the instrument tip comprises a first conductive element and a second conductive element; a coaxial feed cable comprising an inner conductor, a tubular outer conductor coaxial with the inner conductor, and a dielectric material separating the inner and outer conductors, the coaxial feed cable being for conveying radiofrequency energy and/or microwave frequency energy to the distal part; wherein: the inner conductor is electrically connected to the first conductive element and the outer conductor is electrically connected to the second conductive element through a rotatable connection between the distal part and the coaxial feed cable that allows rotation of the distal part relative to the coaxial feed cable about a central axis of the distal part; the instrument comprises an actuator for rotating the distal part in a first rotational direction relative to the coaxial feed cable; characterized in that the rotatable connection comprises a flexible transmission line, the flexible transmission line having a first conductive path electrically connecting the inner conductor to the first conductive element and a second conductive path electrically connecting the outer conductor to the second conductive element. the inner conductor is electrically connected to the first conductive element and the outer conductor is electrically connected to the second conductive element through a rotatable connection between the distal part and the coaxial feed cable that allows rotation of the distal part relative to the coaxial feed cable about a central axis of the distal part; the instrument comprises an actuator for rotating the distal part in a first rotational direction relative to the coaxial feed cable; characterized in that the rotatable connection comprises a flexible transmission line, the flexible transmission line having a first conductive path electrically connecting the inner conductor to the first conductive element and a second conductive path electrically connecting the outer conductor to the second conductive element.