Just as a update, I took the underdash panel off last night.
Cut my thumb open on the rheostat due to the badly angled cut and lack of filing, the 12v socket also broke apart as soon as I touched it.
Anyway, the reason for the "droop" became apparent, the factory only apply adhesive to the middle of the panel, the glue stops about 12mm away from the edge, thus the edge will never stay attached.
I have dropped the panel into a local firm who will powder coat it for £15. I should have it back by the end of the week.
I purchased a new socket and underdash panel screws from BHM,
