- Political Ambassador
Fourth, and most importantly, as noted by those above it doesn't seem you have any actual commitment to those subject areas other than the perceived prestige attached to them. Would you do PPE if it wasn't at Oxford? Would you do "nanotechnology" at an ex-poly? If you want to help people in the healthcare sector, would you consider nursing, or any allied health profession, or only medicine?
You may want to examine your motives for wanting to go into those areas more carefully, and then think about what it is you actually enjoy doing, and what you are good at, and use that as a basis to plan for the future. If you pursue something you have a genuine interest in, you're more likely to do better in it and more likely to distinguish yourself in that area - which is what "top" universities are looking for anyway.