Very late to the party but I've finished! Like many people, we found it difficult (and didn't have much time on Saturday, which didn't help). But a hint for 17a from the forum unlocked the rest for me this evening. I knew the artist, though that didn't help until I got the crosser from solving 16d. I had heard of 22a from reading a fair few boarding school stories as a child (I'm sure the term was used in the Billy Bunter books). COD for me was 11a (with 6D a close second).
At least I don't have to tear the puzzle out and put it in my file of unsolved puzzles.