Highlander009

Sorted!!!!
 
Managed to get the damn thing off at last!
 
Was nothing to do with the tabs, they just hold the assembly together as a complete unit.
 
The "straddle pin" was the key after all.  It's just a spreader like in a plastic rivet or scrivet clip.
 
So, using a small screwdriver or the like, you simply push it through the assembly until it falls out the back of the elbow lever assembly (and promptly gets lost down inside the door frame! lmao).
 
Once this central pin is out the assembly easily comes away from its mounting hole on the door.  I expect it should be easy enough to refit (if I can now just find an undamaged replacement for it).
 
These pics should illustrate its construction nicely:  Front View  Back View
 
Many thanks to hose who took the time and trouble to contribute. :clap:
 
Cheers,
B.