I asked this question of TTTV some years ago and was told that there is no longer any transmission control at Newcastle. The studio feeds go to Leeds and are fed to the transmitters from there. Two feeds were sent, one for TTTV North news and one for TTTV South news. The news gallery would then combine the studio output for single service and split it again for the southern opt. If one of the feeds failed, Leeds could patch in the other one, as has happended very occasionally. At the time the Middlesborough studio also had a direct feed to Leeds as it has been used by YTV in the past - whether that's the same I dont know.
Yes that's true, I was merely pointing out that TTTV Newcastle has one single feed to Leeds, and this has a front-end which has been used in the past to provide partial continuity switching, and can still be used for such a purpose -- for example if TTTV were linking into a programme from studio 1 from news, it is perfectly possible for them to link one to t'other without any input from Leeds. The basic infrastructure is essentially unchanged from when the continuity announcer could link from IVC to the news programme without Leeds providing switching, although this has not been used for this purpose for some years.
The Teesside feed has been independent of Newcastle since early 1993, before transmission was passed to Leeds in fact (prior to Belasis opening the Newcastle tx centre actually had no way of transmitting output from the Middlesbrough studio live; it was passed through the news gallery and provided to pres on tape, who could then opt the Bilsdale transmitter out from Newcastle).
I also asked that if Leeds suddenly went off-air, could Newcastle take over? I was told no, the only site that could do was Manchester but that a single sustaining output would go out to all GMG north transmitters. This was prior to the National itv1 of course.
It's my understanding that Manchester cannot not provide this service either. It has to be said though that *any* gallery (eg news) could be used for continuity at a stretch -- TTTV's news did actually provide a small amount of switching/continuity even when Newcastle was independent, for convenience.