Rang up the KCL admissions office - they said that the average UKCAT score they had for 2011 entry was 650 for applicants that were invited for interview. They also mentioned that a low UKCAT score would reduce your chances, but also that the whole application is taken into account and not just the UKCAT. Tbh, not all too helpful...but that's what they said. She was unable to answer specific (more helpful) questions as only the interview/admissions panel know how they choose applicants.