The firearms law prohibits the carrying of parts of a firearm, because several people could say that they don't have a
gun, but those involved could meet up and build up a gun. This could be the same principle. Applied to a locking knife.
I think you are skating on pretty thin ice on this one. I took the ring off of an Opinel I had thinking on the same lines as you, but was not going to carry the ring, just use the knife like a folder. While having many years experience with knives,
the first thing I did was cut myself badly, when it partly closed on me . It was then promptly binned.