I stepped in and taught a friend's class last week while he was away, and now I need to get paid by the university. But the form requires a National Insurance Number and apparently I won't get paid if I don't supply one. But I don't have one. What is it and how do I get one? Is is the British equivalent of the American "social security number" which you're issued when you're born and is a bit of a palaver to get later on?