Everyman here and hallo! Excellent spot on 21d, and very chastening; fulsome apologies. I changed this clue at the last minute after the test solvers failed to be amused by a preposterous pun (on the N version). Because it's a prize puzzle, we will leave the clue as is and accept both answers.
Many thanks, by the way, to all who solve and/or discuss the Sunday puzzles.