@EightToSixer - UCAT consists of four cognitive subtests and the situational judgement test (SJT).
Each cognitive subtest is scored on a uniform mark scale in the range 300 to 900. Therefore the total score for the cognitive test is in the range 1,200 to 3,600. The median score for the first cohort was 2,400 but this has drifted upwards as candidates do more preparation for it. UCAT is in the process of recalibrating the mark scale to bring the median back towards 2,400 (this will occur gradually over a few years).
The SJT is graded into bands 1 (highest) to 4 (lowest). These indicate the degree of agreement between the candidate's answers and those given by a panel of experts (current senior medical students). The boundaries are based on closeness of agreement, not numbers/proportions of students scoring in a particular range. Less that 10% of each cohort scores in band 4, which is currently the only exclusion used by some medical schools (Leicester, Nottingham, Manchester, Keele, Birmingham).
The way the overall scores are used varies among medical schools. Some simply rank all eligible applicants on their UCAT scores, so the top 1,000, for example, get the interview invitations. Where the threshold lies depends entirely on the scores of the people who apply there that year. Obviously, people with lower scores don't apply to those medical schools (unless they haven't read the entry requirements, which accounts for a few hundred applicants for most schools). Others will set an absolute threshold and either interview everyone above it (so the number of interviews varies year-on-year) or use other criteria to rank applicants who are above the threshold. Others will combine UCAT score with other metrics (e.g. a score for GCSE grades). So there isn't a clear definition of a "good" or "bad" score.