I also found rankings for individual subject at TIMES, (like the one at the GUARDIAN),
I know that these rankings might not be very reliable, but they do give you a good idea of the standards of the universities, also TIMES does the overall UNIVERSITY RANKINGS for the TOP 100 universities in UK:
alot of people i know refer to TIMES when checking the status of any university…but it all depends on your proirities…
good luck