An electrosurgical apparatus for applying radiofrequency energy and/or microwave frequency energy to biological tissue, the apparatus 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; and a generator connected to a proximal end of the coaxial feed cable, the generator being configured to supply microwave frequency energy having a predetermined wavelength λ to the coaxial feed cable; 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 apparatus comprises an actuator for rotating the distal part in a first rotational direction relative to the coaxial feed cable; and characterized in that a length of the instrument tip is equal to λ 2. 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; and a generator connected to a proximal end of the coaxial feed cable, the generator being configured to supply microwave frequency energy having a predetermined wavelength λ to the coaxial feed cable; 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 apparatus comprises an actuator for rotating the distal part in a first rotational direction relative to the coaxial feed cable; and characterized in that a length of the instrument tip is equal to λ 2. 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 apparatus comprises an actuator for rotating the distal part in a first rotational direction relative to the coaxial feed cable; and characterized in that a length of the instrument tip is equal to λ 2.