I don't actually believe super-human intelligence is requiered to do well in a Medicine course, just a lot of memorisation and capacity for learning and understanding a lot of very complex concepts. Although I think motivated C grade students could PASS a Medicine course, and thus become a doctor. I think that with the high risk nature of medicine, only the best should be picked. A Level results do show a persons capacity to learn and understand. Also, even though they may come from deprived areas of London, there is a lot of self-study in A Levels, and the rough students who don't care and hold the class back in compulsory education are very unlikely to be in an A Level class. So, in my opinion, I doubt they'd be able to achieve As in any Sixth Form.
Political correctness is a very dangerous thing, and 9/10 are from ethnic minorities, it's quite clearly picking racial groups too. A patients priority is good health care and potentially saving their life. Seeing a hospital with an equal balence of races and backgrounds is not their priority.