When you are selecting which medical schools you want to apply to, make sure that you thoroughly check their selection criteria, which are usually stated on their websites or is information available upon request to their Admissions Office. Some schools use a scoring system that uses all components of your application (that is, grades, personal statement, UCAT score and letter of recommendation) equally, then rank all applications and use a cut off score to decide which applicants will be invited to interview.
Other schools, however, are more selective in the components they pick and only use the UCAT score in inviting applicants to interview or don’t use it altogether and focus only on the personal statements. You can see how in these terms, what a good UCAT score is becomes very relative. If the schools you are interested in don’t look at the UCAT at all prior to interview, then it would hardly matter what your score is.
Equally if you focus on schools that only look at the UCAT in order to decide whether to invite you to an interview or not, you would probably want to be high up in the 10th-20th percentile of applicants to ensure you get that invitation. Things are somewhere in the middle for schools that evaluate all application components equally and an above average UCAT score will probably be expected there.