Bipolar electrosurgical tool with active and return electrodes shaped to foster diffuse current flow in the tissue adjacent the return electrode

A bipolar electrosurgical tool (40) including a shaft to which active and return electrodes (54, 48) are mounted. The return electrode has an exposed surface (86) that, in at least one direction has a substantially linear profile. The active electrode extends through a bore that opens into this surface so as to extend forward of this surface. A collar (110) formed from electrically insulating material extends over the portion of the active electrode adjacent the return electrode. The collar extend both forward of the return electrode and radially outwardly of the active electrode.