With (more than) a little bit of help from my friends, I've finished. I didn't think I would. So thanks to all who have contributed above.
It was indeed a brilliant construction. I thought there were some very difficult clues; 39 across, 11 down and 35 down in particular. Only one question: was the word in the third row from the bottom needed and did it add anything? As far as I could see there was only final solution - or, once again, have I missed something?
My thanks to Twin and lights out on a very wet sandbank.