18a: It may have rhyme but not reason (8,5)
??E?E?S? ?????
5d: Case for the prosecution (10)
??????T???
20a: Spread found on board that cannot be eaten (10)
????I?L?T?
... except that "accusation" would give me O instead of V in "nonsense verse" and my first E came from "Design in nude sketchily had not been planned, which I thought was an anagram of design nude - undesigned; maybe that was too close to the clue?
AB, that's great, thanks, I'd got accusative, but had completely forgotten the Latin element - 47 years since I wasn't very good at it, anyway! Cheers!