The cost varies by university. You should look at the Registry website sections of the universities you are considering. At my (Scottish) university the total fee alone for such a humanities PhD would be about 11,000 pounds. That's either paid over 3 years if a full-time student, or pro-rata'd over a longer period if part-time. This cost is fees only, and doesn't cover additional expenses, such as buying books, out-of-pocket research costs (e.g. photocopying, microfilming, travelling to archives etc.) and - if studying full-time - living/maintenance costs.