As you have only mentioned very competitive and quite prestigious universities, I think you should remind yourself of all the other options for University choices, which can provide just as good an education in the subject. Queen's have a ranking system in which your UKCAT score and UCAS tariff are awarded points in a 50:50 ratio, your ucas tariff includes predicteds, GCSEs and a couple of other qualifications e.g DofE, music exams. Theoretically, this could mean a very high score may compensate for GCSEs that aren't a clean sheet. Kings asks for a high UKCAT and A*AA, in fact all the universities you mentioned ask for those A levels. I don;t know how much weighting Imperial put on GCSEs but I think King's ask for quite a lot, maybe contact them? With your GCSEs and a good UKCAT score, you could have a very good chance of interview at many other universities, maybe you shouldn't limit your options to these unis at this point.