If you're interested in Durham, or even if not, be sure to check out the Dunelm Road blog. It's a multi-person blog written by several American students who have studied or are studying at Durham, and includes a lot of invaluable information about the U.K. academic culture, funding, the difficulties of moving overseas, and anything else you might expect in such a resource. Even if Durham does not wind up being your school of choice, it can be a good resource to orient you toward study in the U.K. There are good blogs from other American students at other institutions, as well.
From what I understand, the key to finding a landing place in the U.K. is to be in touch with a professor. Identify people whose work you know well, and whose interests match yours, and e-mail them with a proposal for a dissertation. When you find someone who's interested in supervising you, apply to the school. My impression is that U.K. institutions are eager for students at the doctoral level, especially since they do not have a great deal of institutional financial aid, and your presence at the school (whether you pay for it yourself, which is most likely, or earn a grant or fellowship from some outside source) will bring money into the institution. That said, I know of many people who have had great experiences in U.K. schools and wonderful mentoring from the professors there.
It's an appropriate option for people who feel they have had enough coursework and are ready to begin a dissertation right away. If you're not that sure of yourself, or if you would prefer a better guarantee of financial aid, the U.S. or Canada have more to offer. The Toronto School of Theology might be worth looking into, for your interests, as well as Boston University.