I'm not in the UK or Britain but from other forums and a friend, I've come to understand how it runs. For English, just read and read and read. My English was pretty poor when I started school. Parents were working and my grandmother who baby-sat me spoke horrible English (although my parents speak English perfectly). Anyways, just read and in addition to that, why not try going to an online forum that's meant for objective debating. You'll not only broaden your views on whatever subject but it allows you to engage in the literature you're reading. Even on PC, if there's a thread devoted for a debate or discussion, then hop in, same with the chat. Or if you'd rather not join a debate, go to a bookstore (preferably a used bookstore to save on cost) and buy whatever books. Try to buy from a variety of authors who write different genres so you can get a nice diverse sample.

For science and math, lots of it comes down to having a good instructor, book and a style of learning that meets yours. If you have certain questions about a topic or a math question, then post them here (or another forum) or ask in real-life.

This year (my third year in university) I'll be a facilitated studier/advisor, which is basically when an undergraduate doesn't get paid but they help explain whatever in the course is not making much sense to the students (generally first-years). You sometimes can be able to look over their papers but you cant grade them nor can you tell them exactly what to do. It's optional for the students to participate in. I'll be doing this for biology, so if there's a question on science (including other non-biology sciences), I'll try to explain it coherently.