Hi, thanks for the reply. I have refitted the ring and put it all back together for now.
Plus, I think I've found the issue.
Despite everything and everyone telling me it was the correct part, it seems it may not be. I've also found this: BREMBO Brake Disc SOLID 08.5833.25
compared with: BREMBO Brake Disc SOLID 08.5834.25 SINGLE Disc
If you look at the drawings you can see that a subtle difference between Brembo 08.5833.25 and 08.5834.25 is the ABS ring mounting point diameter.
It seems (in the tech drawing that the part where the ABS ring fits is 75mm (08.5834.25) instead of 72mm (08.5833.25) which is about right in my estimation. This looks to me to be the correct part, but does not show up when I put in my reg number on various sites.
So looks like I was sold the wrong discs (with missing ABS rings) and it's probably too late to do anything about it now. I guess I'll have to order the right discs.. more expense..
Moral of the story is don't buy a car.. I don't have these issues with motorcycles (at least it's very rare!)
P.S. anyone wanna buy a pair of Brembo discs, part number 08.5833.25 with fitted bearings but no ABS rings? Haha..