An electrosurgical resection instrument (100) for applying to biological tissue radiofrequency electromagnetic energy has a protective hull (120) comprising a shaped piece of dielectric material mounted to cover an underside of an instrument tip (104) of the instrument (100). The protective hull (120) acts as a shield to protect tissue that may lie under the instrument tip (104) from damage during treatment. The instrument (100) may be particularly useful in procedures performed in a gastrointestinal tract, where bowel perforation is a concern, or in the pancreas, where damage to the portal vein or the pancreatic duct may occur when a tumour or other abnormality is being resected, dissected or removed.