Well, this was the easiest fix in history!
I've had a really annoying rattle from the rear of the car for a while now, and last week removed the parcel shelf.....and the rattle stopped.
I was going to get a new shelf from the dealers, but when they were looking on EPC, they said to try replacing the plastic stops on the end of the shelf. They are what hold it in place while the boot is closed.
3 24455455 2236967 -CLIP,LOAD COMPARTMENT COVER 2

Replaced them as soon as I got home, and it's fixed the problem. They were only 70p each + VAT (y)