What are widely-used UK-English style guides?
In the UK, what are the equivalents to Chicago Manual of Style, the Associated Press style guide, Yahoo, APA, MLA, etc? Most importantly, what are their intended audiences? (AP is used for journalists, Yahoo for the web, APA for academia, et cetera.)
I'm specifically asking about style guides that are structured like indexes like the above references, as well as books that compare US to UK english. (The Economist style guide, for example, has a good section on this, but it's also quite short.)
(Note: I'm aware of this general question on style guides, and I'd have no objection to this question being folded into that one eventually. For now, I'm posting this as a separate question to get some attention to the question of UK usage.)