Medical screening is 'in confidence' even for the recruiting personnel who process applications past interview. A general GP medical is undertaken and any issues that may arise are then looked into for a 'Specialist Medical', so the information would be sought to clarify your history - e.g Asthma, severe fractures, illnesses, medication for mental health, poor hearing, mobility. The medical conditions that may prevent you joining are defined on the recruiting website. I hope that this helps.