That's Mike Partridge proprietor of Walridge Motors.
When you say it is a "21 inch mudguard", I assume you mean it is made for a 21 inch wheel?
Did you source the mudguard from Mike as well? If so, I would give Mike a call. Obviously something is incorrect, the stays, the bridge or the mudguard.
'73 MkV 750 Roadster
'74 850 Interstate
some Nortons in boxes