All was good until about a week later when the rear-door wouldn't open anymore... oh no!! I climbed in the back and had a look. Since the door was effectively locked shut then everything is nasty and difficult.
I was certain of the cause... glass in the latch mechanism. How to get that out?! I tried lots of stuff for many hours and here is a summary (with success!)
Step 1: Check the easy stuff...
The latch and electric locking mechanism is at the bottom centre of the door and has a cable running to the door handle
Try locking/unlocking the car. The white piece of plastic on the latch mechanism moves up when locked and down when unlocked. No problems with that for me.
Get someone to squeeze the outside handle - the cable should pull a lever on the latch/lock to the right. Try pushing it directly to see whether it can move further (the cable could be stretched or not attached properly). Again nothing so simple for me.
The picture of the lock/latch mechanism was taken much later when I finally got the door open.