Cardiff Uni late deferral

So, I got into Cardiff Uni for english literature. I screwed up big time when it came to my exams apparently, and scored a lot lower than I've ever actually managed before in mocks or whatnot. I actually missed my Cardiff offer, as my offer was BBB and i got a BBD with an A* EPQ, which probably considerably helped things. Regardless, I still got an offer from Cardiff. However, I was wondering if under these circumstances it would possible for me to have a late deferral for a year? What would be the chances?

I wrote an email (or am in the process of doing so) to Cardiff admissions listing two reasons:

a) To take a gap year. Working, travelling, building a writing portfolio and developing my writing. Typical gap year things basically.
b) It would cause a lot of hassle moving GP providers during this time because I'm pursuing a medical diagnosis.

Any help appreciated.