For me I was way off the needed grades, I still got in, and my course was over subscribed that year. But I went travelling in my gap year, and wrote my personal statement myself, so I think my application may have stood out a bit?
I was told that (for the economics department at least) they have way too many people applying, so they're going to get stricter on admissions. Also I think Portsmouth is the most improved uni in the country in terms of people applying (ie. percentage increase in numbers applying), but of course it all depends on your individual department.