to be honest what do we know- we're just applicant/students, not the interviewers, we don't know how they'll percieve you if you apply and have an interview. so go for it, u never know u could strike lucky. however it has to be something you actually want to do- don't just apply because it's oxbridge, you have to LOVE the course and the place as well (in my case it wasn't so much the course, rather the gorgeousness of the city)
it does come across as though you really haven't thought about uni properly- you're just going on what your parents/teachers are saying (please correct me if i'm wrong). the thing is though, you want to do medicine- there are loads of unis that do a good medicine course, places like Manchester/Leeds/Newcastle/London uni's/Liverpool etc etc are all great for it.
my advice would be to a) work damn hard to keep your predicted grades(or better) next year- you're at a disadvantage for applying ANYWHERE if you don't. and research research research. open days are there for a reason,as are medic conferences and courses like medlink, and local anaesthesia days etc (dunno if anywhere else apart from my local hospital has these?). oxbridge isn't the be all and end all. there's loads of people out there who could apply to oxbridge, and would probably be successful, but they don't want to, cos it ain't for them