It was called RBS, the BBC’s main transmitters had ( where possible) and alternative source. My local Tx Hannington which was off air fed by Rowridge, had Crystal Palace as an RBS source ( for the BBC, and Mendip for C4)
Lower order transmitters and relays had no back up source should the parent die.
ITV and C4 used to have a backup transmitter for London/SE at Croydon in the event of failure at Crystal Palace. IIRC it was actually fed from one of the Meridian transmitters (possibly Hannington?) as on occasions when it was tested you would get ITV/C4 South Teletext and pressing Reveal on P100 would show the Rowridge three letter transmitter code.
Right, now, hold tight. You're quite right there were back up analogue transmitters for ITV and C4 at Croydon (later, from about 2006 for BBC1/2 too, but that's another story). Because the Teletext
(from now on in this post, referred to as 'Teletext') server/inserter for London was at Crystal Palace, that would obviously vanish in the event of a catastrophe at CP. Therefore at Croydon there was a data bridge, that took the Teletext data from the Hannington RBS receiver, and inserted it into the incoming video feed from LNN.
If both LNN and CP were to ever both suffer a catastrophe ! then Hannington became the video source (same mirrored arrangement for C4 of course)
Hannington itself, that was line fed for the Meridian North region, had a data bridge that took Teletext data from the Rowridge RBS receiver, and added it to the incoming video feed from line.
If Rowridge suffered a power glitch, the Teletext server there appeared to have no UPS, because it would take 10 mins or so for the carousel of pages to rebuild again from scratch. I think the servers were fed from Teletext HQ in Fulham by 9.6k data lines ?