Finally, both the spare wheel hanger and the spare wheel key were in my possession!
So the first think I decided to try was to make sure the spare wheel key fitted... Nope! The bumper is in the way... Oh well, it is made of metal, it's not far off and metal is BENDY ... One hammer, whack whack whack whack ... Yes, now it fits! In it goes ...
CLUNK.
Ah bugger! Maybe the handle is not at the right angle to fit through the hole for the spare wheel key? Fiddle around... CLUNK clunk CLUNK.
Hmm.
Withdraw the spare wheel key and look at the van more closely...
Yes, some bugger has welded a big bit of repair plate across the hole. There is no hole

Somehow, this fact escaped my notice until now.
When I get a chance at the weekend, I'll get the electricity down to the van and get the electric drill on it, and drill out, file off and then Waxoyl a new hole. The new hole will probably be square because that's easier ... Gah!