Right...
OP- Do the one your best at because (rightly or wrongly) you need to get minimum AAB. Physics or Maths doesn't matter as you have chemistry and biology, but possibly be careful when applying because some Uni's want a chem, bio and a non-science, so maybe don't apply there
Chemistry is seen as more important than Biology because biology involves lots of irrelevant stuff and because they teach you Human Bio anyway.
As for media etc I haven't got a clue how the Uni will see it, but do know of someone accepted onto the 5 year programme at BL after doing a drama degree, so accademics aren't the bee-all and end all. Just be prepared to justify your choices if asked, for example- I chose media because I thought it would be a piece of cake = bad. I chose media because I believe it provided me with a better insight into how to get my ideas across in an appropriate way in a world that is very media orientated (or similar)= better