There is no central credit score — each lender (or credit agency) creates its own sets of rules as to whether you're good or bad, all with different criteria. Some of those may package it up as a "score", but that's essentially meaningless. Checking that your credit reports from the major agencies (Experian and Equifax are used by about 90% of lenders IIRC) are accurate is worth doing from time to time, especially if they're offering it for free (although as the maximum they're allowed to charge, by law, is £2, be careful that the "free" version isn't a way of sucking you in to something else)

http://www.moneysavingexpert.com/loans/credit-rating-credit-... sets it out quite well.