Hi all, thanks for the responses. Sadly in spite of directing my attention to West Africa I have been unable to find a similar example; Martin if you have a chance to snap a picture of yours I'd love to see it!
Tim thank you for your pictures. I was watching the monitor lizard as well and I'm glad a forumite got it. I am attaching more pictures, with a genoui from Morroco for comparison. I know very little about bayonets but the genoui definitely has more of a bayonet sort of feel than does the "ballock". The "ballock" has a far greater profile taper and also a substantially different cross section.
Also just for fun and comparison, I'm attaching a picture from
here showing some "dungeon daggers" which most closely resemble this one.
Thanks,
--Radleigh