Depends. I go to a community school, which has a set uniform policy (it's not as strict as other schools though, as we don't have blazers and girls can get away with miniskirts). We're not allowed to wear skirts without tights, though, and not shorts unless it's for PE. No jewellery either.
I think in private schools and boarding schools, you can wear whatever you want. Idk though, because I've never been to one.