There are a tonne of boxing gyms around, and some offer student discounts so you won't be hated. Just search to yellow pages when you get here, or you could join the university boxing club - both unis train at Toughguise II near Infirmary road and Shalesmoor. You might want to try a few different gyms out because each gym has a different atmosphere. For example one gym might be full of aggressive meatheads that use strength and size over technique => probably not suited for a beginner. A good gym will drill the basics into you every session and will teach you to use your jab and box on the outside initially. As you get better, you'll adopt a style that suits your physical size and attributes.
This is my sales pitch:
One MA that embodies FITNESS, physical conditioning, self-defence and spiritual elements is Muay Thai. There's a club you can go to called Wicker Camp. They'll teach you from scratch, and if you go regularly (unlike me), you'll find that you can progress very quickly as your physical fitness improves. Although the techniques are powerful, it's a really fun and in some sense, relaxing art to learn. It's very easy to become totally immersed into the culture of Muay Thai, it'll make you want to go to Thailand!