Lots of people are criticising the UKCAT, but research has found it to be a reliable proxy for A level RESULTS (as opposed to predicted grades). Also its results aren't skewed by which school you went to, whether or not you have a tutor, how many times you resat Chem3, how many A levels you sat (some people sit five academic A levels plus an extended project and STEP just for a lark, some people do just 3), etc etc.
In any case, some Med schools don't use UKCAT (Birmingham, Liverpool, Lancaster, Bristol, maybe others too): apply there. And you surely can't criticise the well-respected BMAT? There are four undergrad Med schools that use the BMAT, hows about you apply there? (BTW - among my friends, those who acheived a high UKCAT also scored a high BMAT and the same correlation held for low scores, but that may be a skewed sample).