Wow, this is a revelation. Well, maybe that's OTT but I just found out you can renew library books, check any requests, and get notified by email for any overdue renewals on the internet nowadays. Well, at least in Surrey. You need your card (with the number) and a PIN code you can get by request from the site or by popping into your library and asking. If you're in Surrey go to the Surrey County Council's website. Don't know about other counties but it's worth a try - google it or something, it might be www.<countyname>cc.gov.uk.