I know this is an old thread, but it has been bumped recently so I thought I'd share my experiences!
I applied to do pharmacology and molecular genetics, I missed the Jan deadline but I applied in late April/early May time so before clearing. I did a foundation year at the University of Greenwich and received a conditional offer requiring 70%; I actually scored 69.4% but still got offered a place. A couple of people from my course at Greenwich applied before the Jan deadline and they both got straight rejections; the only thing I know for definite that made my application stand out compared to theirs was my work experience*, and possibly a few particularly good marks (into the 80%s and 90%s) which I drew attention to in my personal statement.
So it's possible to get in off the back of a foundation year, but I think you need to have a little something extra on your application to make yourself stand out.
*I'm a mature student and I had 3 and a half years of NHS work as a lab assistant in haematology and biochemistry, plus another 2 years working closely with microbiology, and I was allowed to work a friend who is a post doc researcher for a couple of months, which gave me experience of working in a research lab.