"Guest Ale" is just another synonym for Real Ale, Cask Ale, call it what you will but it probably was English.

Cask ale isn't usually cold as in "condensation forming on the glass" cold (like a Fosters would be), but it's usually served cool or a sort of neutral "not really cool or warm" temperature. If it's literally warm, then that's pretty much a crime

A beer is only as good as the place that serves it. Most of the crap pubs have been wiped out by natural selection (aka. the double dip recession with extra suck that we just had) but of course, those overpriced minimum effort airport bars aren't going anywhere.
If in doubt with a cask ale (hand pull, to give it yet another name, as they pull the beer through using those massive lever pumps, you see) ask to try a sample first. Pretty much any pub serving cask ales will do that (unless they suck and deserve to die, but see previous point about the positive parts of the recession).
I sometimes also ask if anyone else has been drinking it. If you're the first, a good pub will pull some through first, but some will just give you the warm beer that has been sat there in the pipes.