[Technologist]

There were occasional splats on the BBC as well, or at least hard-switches where the vision and/or sound momentarily glitches, but these were usually about a minute before the opt rather than on the second. BBC NE was particularly bad for this; you could clearly see the switchover, there would be a screen tear, and the picturewould often shift to the left/right and/or the colour saturation would change. Sometimes a small sound jitter as well (repeated or lost frames). It may have technically been genlocked, but clean it was not!

The BBC region would opt by taking the Network (now sustaining) feed through their mixer - then pressing the OPT switch - thus they could (elegantly) Mix or lead sound into their local programme
-  hence a splat perhaps before the actual opt point
and may be one after they opted back as they took themselves out of circuit.
of course if they genlocked there should be no problem ....   

But as the whole station had to be genlocked and with more VT editing which required stable pulses
.. the advent of the Synchronsier was a good thing ..except!!! ... ideally you needed two
One on the Mixer input so that Network was synchronous on the mixer,
the other on the local side of the Opt switch genlocked to the other input (Network)
so that the mixer out was synchronised to network

BUT  a region was lucky to get one....
It put two frames delay in the network feed which meant repeated or dropped frames
(think of the stutter you see when going to the red screen of death)
and in those days compenstating audio delays were not normal!!
so you lost lip sync!
so nearly always the possibilitity of a splat.
....and BBC Newcastle was well known for having more than most!

The other thing was that the opting/ network arrangements in
each region were different.... this was unified in the mid 1990s
when DCSIS/Stereo, Lambie Nairn Network ID, Regional Ceefax, Regional Recall,
new Pres desks, Regional subtitling and some other Techy things were done
to a common design  and implementation which solved most of the probelms. 

I think by the end most ITV stations had text services on 600 but they weren't there from day 1. 

The first I saw was that summer when I was down in the Westcountry area. I think theirs might have been done in house, whereas the other regions used Intelfax. Carlton/LWT and GMTV were late 93 I think 

Channel 4 and 5 had theirs too on p400 and p500 respectively. 4Tel was very minimal on day 1 and grew a bit although nothing like what they had pre-1993. Channel 5's was there before they even launched with transmitter details

None of those were part of Teletext (capital T) and were added with subtitles at the TV station, hence they had different headers

There was the Ancilliary teletext service which (when providied) was on lines 21/334
and line 22 as subtitles were on line 335.

The purpose of this was to provide programme related information
- like listings, the recepies ,  contact details, other back ground on programmes
(and may be some news!!)  and PDC triggers
It was rather patchy as it cost each itv company to do it ....
so some did not / took their time! 
and then even when they had it tended not to promote it on screen
so few knew of it!