I have found this guide in the Tutorials / FAQ:

To remove the bee sting aerial that is situated at the rear middle of your roof you must open the boot lid and look to the final part of the roof lining that appears at the rubber seal.
Take out the three clips that are postioned along the edge (Simply try and use your fingers and a flat headed screw driver to pull them out, they ain't screwed in just pushed in) and peel back the roof lining which you will find is very easy.
You will see where the aerial comes into the roof and a bolt with wires going up to it is there. Simply take a 17mm spanner and undo this once undon the aerial will pop off and you can get into it to do whatever you need to do. Replacing simply involves reversing what i have just said.

But can anyone tell me if I need to remove or loosen the panels where the rear seat belts are held into, the head lining seems to go behind these?

Anyone have any tips before I attempt this?

Cheers

Jon