Thats one of the things that baffled me. We still have Departure CCTV (oh the old days in teh darkened room sleeping off hangovers) or DETS as it is now...but only at TC. NERC have no access to it - even during FLOP/SwIMM when it becomes essential. Can anyone explain why NERC don't have access?
As far as I know it was never a "system" requirement. It was possibly an oversight in the requirement set. You don't ask for it you don't get it.
Cost is also very likely. At West Drayton TC was next door to AC so you run the cable from one room into another. Now you have to run the cable 60 miles, piping a TV picture this distance becomes very expensive!