A lot of how we chose our Universities was the universal RAE ranking system, which ranks each University's research excellence in various fields. Generally, a very good sign of how good a program they have in each field. Since you're probably not familiar with the reputations of UK Universities (I know we weren't), this sort of thing can be very helpful.
We didn't see your field on there, but you may know where to look for what you want to study. If you check out the RAE, you should be able to tell which Universities are the very best at your field. From there, you need to decide what city you want to be in, and so forth. Here's the URL:
http://www.hero.ac.uk/rae/rae_dynami...ults/byuoa.asp
Hopefully that will help, some. If not, we can see how else we might be able to help.