How to remove B post inner plastic cover/panel?

After a disagreement with the garage door and the silly mobile aerial on the roof... I need to drop the headlining at the rear to gain access to the aerial cable. My question is, how to I remove the plastic panels that sit inside the boot over the B pillar (i.e. between the boot opening and rear side glass).

Having tried gently pulling I have managed to break off a plastic clip, so before I completely destroy the plastic cover/panel I thought I would get some advice.

Thanks,
James