Thank you Meursault. All a bit fiddly, I'd say. I'm still not clear about 17, unless STER(n) is intended - and if it is then I don't think much of 'Left' as a reversal indicator.
Other weaknesses: 'seem smaller' in 19 isn't justified by Chambers, which gives the answer as vt only; and 2 (after subtraction of the extra letter) was just a straight - if artful - definition clue of the type found in The Times or similar puzzles, not in The Listener.
My final grump was with the preamble, where 'apart from its last word' could have avoided unnecessary ambiguity. I expect others will think these criticisms unfair or irrelevant.