To the Op, take your time, think thoroughly about it and maybe discuss it with some family and friends. Seeing as you've done so much experience and research into medicine I'm sure you know that different doctors can have very different jobs, depending on their speciality, whether they do research and so on. Because of that, it is likely that there will be something you are really interested in or would like to do.
To everyone else, I have an offer from a British University, however I also might have some offers from other international universities to study medicine. My problem is that I will get some of these international offers after my deadline to reply to the British university that has given me an offer. If I firm my UK offer, can I still decide not to go and instead go to one of the other universities outside the UK that has given me an offer? Or, is there some penalty/ I have to definitely go once I've firmed the offer?