Thanks for your replies.
Yes it's the Strap mount that I need. There are plenty of straps around that will work, but the mount that connects to the camera is a sort of bayonet clip(?)
It does seem as though it has been designed just for the Canon waterproof cameras(?) because I can't find it anywhere else. But it is quite hard to search for!
I was kind of hoping that someone out there would say "oh yer, you can get that connector from......(sports/gadget/climbing/sailing shop)" Then I could get one and attach anything I want to it.
If anyone knows any different, let me know.............