Anon,
It's pretty chilled out at UK universities. People wear what they want.
Clothing does depend a little bit on what you are studying e.g. if you are studying art, you might be more creative, expressive or grungy and if you're studying something like podiatry/ physiotherapy you might wear more sportwear, but in general you can just be yourself.
It might be a bit different at Russell Group universities/ some of the universities with the bigger names, it might be more smart casual, so you can always go smart/casual on the first day and then you could get a general idea of how people dress on your course.
Hope that helps,
Oluwatosin – 2nd year student – University of Huddersfield