BEagle,
The CAA reference number is nothing more than that. It can be on a PPL, a CPL/ATPL and an ATC Licence all at the same time.
There is no requirement for one to give up one's valid for life UK PPL when one obtains a JAA CPL or ATPL.
Your Statement that ;
"Only non-instructors on the CAA staff will have signed licence rating pages."
Is totally incorrect. There are what the CAA call "R" examiners and I know of at least one who is not and has never been an instructor of any sort.
Doing an admin job does not require instructor skills.
Regards,
DFC