I agree Jack, this was a brilliant construction. The reservations I expressed earlier about the endgame were down to me being thick rather than any fault of the setter.
A mate's Dad (who was a lovely bloke) was a keen practitioner of the theme and I think that by the time he died a few years ago, he'd done it in pretty much every possible venue in the country. He'd have loved this puzzle and I wish I could have called him for help!