The UKCAT is used by most medical schools, but not all of them. Plus, the ones that do ask for it all use the scores in different ways. Some Medical schools choose a score which they use as a cut off when determining who to invite for interview. Their websites normally say if they do this and what the cut off is- if your score is lower than this then it is not worth applying here. However, some Medical schools use the UKCAT scores to give candidates points but they look at everything else on your application as well. So although you may drop a point or two by having a low UKCAT score, your academic grades or other achievements could mean you pick up points that a lot of other people don't. Getting a low UKCAT score is not the end of the world it just means you need to be slightly more tactical in where you apply. It is only a small part of your application, you'll have plenty of other great things to show you're a good medical school candidate.