I suspect a typo too. More likely ATV or Anglia as the 'other' backup . If Kent house were evacuated etc the switch would have been at BT tower, not CP or Croydon, so no need for any off -air signals.
Although Thames once had a bomb scare evacuation, and on that instance the IBA Croydon ROC patched off-air received TVS to Crystal Palace (Remember up until the late 80s, the outgoing BT Tower feeds went via the IBA control room at Croydon on their way to CP).
I think during Southern's era the same thing happened one Friday night with LWT ?
I wonder why they would have done that? TVS’ output would have been freely available at BT tower?
They may well have initially patched in the off air feed at Croydon, because that would have been instant, then
made phone calls to BT and TVS to get TVS routed via the BT circuits ? The received Hannington pictures at Croydon were very clean (cleaner than many permanent RBL links !)
Don’t know about LWT>Southern, I would assume LWT>tower>southamptn local SWC > transmitters?
The LWT thing, was in the same direction, Southern being seen in London.