All done, with thanks to a variety if tips, for which many thanks. The one which finally cracked it was getting the letter for 18d. Several missed opportunities before that -
I had the 4 th and 5th letters of the message, but couldn't make sense of them
I guessed who the ravishing actress was, referred to earlier, and mentally thought of her films but didn't hit on this one. There was, incidentally, a stage musical as well, which was dire!
An hour after finishing, I suddenly clicked as to how the 24 clues were thematically placed! A nice pdm!
I'm still baffled by the wordplay for 45,46ac