Originally I had a different answer for 10a (using the usual 2 letter 'party' and the single letter for 'with') but after I'd made the thematic change and couldn't see 'Guardian setters' as a definition in any of the clues, I gave up on it.
a really fun solve - under 3 hours too, so not too time-consuming. Was about to remark on 27 being both an anagram and a synonym of speed, then realised it was thematic and my original anagram was right but needed treating ... clever
I am also a little unhappy about 12a. First the unmodified solution seems to require American spelling. Also the two letters requring modification are not the standard spelling.
9a does give an element, but after modification I don't see how what results could refer to a side effect of consuming it. Unless consuming it is very boring.
Noddy (of the British band Slade) was noted for his record titles like - Mama Weer All Crazee Now' (I always thought it was an anti-skool-spelling stance but i'm pretty a homophone is what's wanted here).