Chris, "defunked" reminds me irresistibly of Radio 4's wonderful "I'm Sorry I Haven't a Clue" and their game "Uxbridge English Dictionary":
Barry Cryer: "Defunct: to have one's rhythm removed"
Sorry...
I think Bob Stanford Tuck was responsible for a couple of Luftwaffe bombers that ended up in the Bristol Channel, probably about August 1940 if I remember his auto-biog correctly. He was based in South Wales (Pembrey?) at the time. I wonder if anything survives of them, though I expect they are in deeper water and maybe further down towards Lundy.
Good luck with your searches.