Many thanks to Charybdis (and possibly also Monteverdi). Some fairly gentle clues and the first part of the endgame raised a smile. However, I couldn’t initially find what I thought I was looking for in the grid. Went out to an absolutely cracking performance of the Monteverdi Vespers by I Fagiolini as part of the Lammermuir Festival and, in the middle of the Magnificat, it struck me that if I was looking for a “dumpty dum” that might also be phrased as a “dum of dumpties”.Got back home and lo! It was so.