Not 100% sure on these things but here's what I know (I think!):
Sheffield want a very strong personal statement - not sure how they view UKCAT.
Nottingam say that roughly 25% of their "do we interview them" decision on GCSEs and the other 75% on UKCAT, so a good UKCAT makes up for not great GCSEs and vice versa. They dismiss anyone who gets Band 4 for their SJT straight away.
Bristol don't look at any aptitude tests and base a lot of their decision about inviting you to interview on personal statement, so you need a good one for them.
Cardiff look at a range of things, but if you get to interview then you really need to know your personal statement well. They don't look at UKCAT very much but they use it to differentiate between very similar candidates when deciding who they interview.
Birmingham is similar to Bristol in that they don't look at aptitude tests (although this is changing soon I think), but the personal statement is just part of what they look at - you need very good GCSEs (a good few A*s, some in specific subjects) and 4As at AS level.
Kings College London want a very good UKCAT score - I think 710 is what they want this year - and like good GCSEs. Not sure about how much they look at personal statements.
That's most of what I know - I'm not sure about other unis, this is what I know from going on a hell of a lot of open days and from my friends. Hope it helps!