I have finally staggered over the finishing line, but with a completely frazzled brain. 24a was my very last solve, and having entered 21d in the wrong sense had me flummoxed for a very long time. For 20a, and not having the OED, I have assumed that the consonants in the second word are in reverse alphabetical order, confirmation of that would be greatly appreciated. It appears that having to cold solve many clues is becoming quite prevalent, which is extremely frustrating as it seems to contradict CROSSWORD - but hey ho! Finally, as the PDM came a little late on for me (should have read chambers for the 5 letter set group), there seemed to me to be an unfair number of unches. Still, it is a brilliant puzzle, and I would sooner have niggles over the complexity and high difficulty than the ease of the completion.