That YTV one was interesting for the LWT colour bars. I think that's been on this thread before, but I would suggest that either YTV was showing it locally, and British Telecom, trying to establish the feed again routed things to LWT by mistake, or LWT was networking it.
Interesting they went to the Independent television breakdown caption, as opposed to a YTV caption. I always thought that it had to be black sent to the transmitter for 30 seconds before the transmitter took over. That wasn't 30 seconds!
I would have thought the caption at the transmitter would appear when there's a lack of video rather than black video. 30 seconds of that seems a long time. It looks like the line that went down was between YTV and the transmitter(s)*.
The circuit out of LWT was either a mistake, or some sort of work around, with the output going down to LWT and then back up to the transmitters.
*of which they had more than one, so either they lost everything out of their building or everyone saw the captions even if they weren't watching the transmitter that went faulty (which presumably is the one they can watch off air at Leeds - Emley Moor?)