There will be 3 interviewers, a chairperson (senior interviewer), a GP/consultant/SpR and a medical student (year 3 and above).
Each member of the panel marks you out of 15, which is 3 marks each for communication, motivation and insight, responsibility, social awareness and interests. So theres 45 marks for the interview. This year you needed about 37 marks for an offer (not including ucas form).
Generally, the questions are pretty specific. They may ask you to talk about a recent news topic, they will certainly ask you questions regarding your personal statement, especially work experience, so definitely look over that again. An socio economics question could pop up, like, regarding health problems in a specific area, eg, TB in East London.