New one on me too.
As the scabbard wouldn't fit into a 37 Pattern frog, the bayonet would have to be carried "fixed" with the scabbard on, Russian style.
Another thought: Helves of post-1942 entrenching tools sometimes had lugs on the end so that a bayonet could be attached and used as a mine probe.
Can't imagine that this contraption would make a better probe than a bare pig sticker, but I'm finding in hard to get inside the head of the character who decided to put a ring around the scabbard.
BTW, post-war, thousands of pig-stickers (unadorned) were sold as tent-pegs.