Hi Phil,
I have been having a look to see what I can find in the parts book.
It is clip number 4562113
I only have a wagon so have not seen inside the boot, but if you cant get to the back to put a nut on you might need to make up something.
Rare spares do sell a clip with a 22mm side which will slide in behind the moulding but you would have to glue it in position to the back of the
moulding first, and then push into the rubber gromets.
Just my idea of how I might tackle the problem.
Hope this might be of some help. PM me with your phone number if I can be of any help.
Cheers Stewy