An electrical surgical instrument has RF electrodes and a gas conduit so that a plasma can be formed at a distal tip where a retractable surgical snare 338 is arranged such that the thermal plasma may be directed to biological tissue encircled by the snare. The RF is delivered to the tip electrodes via a coaxial cable 302 in the body of the instrument. The RF may include microwave frequencies and the probe may be fed from separate RF and microwave sources (204 206 figure 2). The snare may be cold snare (fig 3) and formed from an electrically insulating material. The snare alternatively may be electrically active (fig 4) and connected to receive RF energy to be radiated into the area encircled by the snare. The instrument can be used in different modes and configurations (see figures 3 and 4) : (i) a plasma to perform surface coagulation, (ii) a non-ionising microwave field (in the absence of plasma) to perform coagulation at a deeper level, and (iii) an RF field to assist with cutting. The RF electrodes 312, 318 may be relatively moved (figures 4a, 4b) when the non-plasma mode is used.
