"If the PIC has left his seat to re-set the CB's surely this would have been picked up by the CAM mike, and probably also it would have been discussed."
It surprises me that someone has not commented on this before, I've seen comments that the PF was slow to react to the 56 degree left bank, but if the captain was busy sliding/falling around due to the increasing bank while out of his seat then maybe that explains why the FO didn't react, he may well have been looking back over his shoulder and thinking "Oh crap!"