Hey, sorry I felt like I kinda waffled on a bit in previous post, but I'm glad it was helpful! I'm a mature student so my entry path into UEA wasn't really the normal route of A levels and predicted grades and all of that stuff. I got in through Open University. I was invited to an interview though, which was fairly informal, we had to analyse a poem, but it was mainly just a chat with one of the lecturers. It mostly revolved around what I had written in my personal statement. I was fortunate that I'd done some teaching in China so we talked about that for a bit. I think he also asked me about what poets I was into, as I vaguely remember rambling on about William Blake! A few days after that I was invited to submit a portfolio of work. I can't remember exactly how much they asked for now, but I think I gave them about 5 or 6 not very long poems, but you could also submit prose, or a combination of both. But just make sure that what you give them is the best it can possibly be. Read, re-read, edit, get other people to read it, edit some more. I seem to remember that they didn't give a lot of time to get the portfolio to them, maybe 3 or 4 days, so make sure you have stuff in reserve!
I don't think everyone gets called to an interview, especially if they're coming through the more conventional routes, but I think everyone has to submit a portfolio. UEA does seem to want to uphold its reputation as a premier creative writing institute, so yes they are looking for work that has potential. That's the key word. They're not looking for polished writers. They're looking for those who have put the effort in and who show a willingness to learn.
Sorry, more waffling. I've read too many books! Anyway, hope this helps! Let me know how it goes.