dis3 - I think technically yes, Gordon gets first go, but if it's clear that he's not going to get a deal then he may resign, at which point it's open to other parties to form a formal coalition or go it alone with a Queen's Speech that attempts to get enough cross-party support to get through.
I THINK. Really I have no idea what I'm blithering on about.
Dunno what happens if GB can't form a coalition but still doesn't resign. Presumably he presents a Queen's Speech, it gets voted down and he gets dragged out kicking and screaming?