[Stooky Bill]

How did the GMTV ancillary service work then, since their route to transmission was via each region (unlike TVam)? In Central land I seem to remember page 600 (and the header legend on the ancillary range) would change to GMTV Text between 0600 and 0925, but all the other pages of Centext would still be there.

Was this just something each region handled on GMTV's behalf?

My understanding is that at the regional centres their presentation area was switched out of line during GMTV and the signal path went through their news gallery.

If so my guess would be that the teletext for each company was added before that switch and GMTVs passed through the gallery. Therefore the teletext service broadcast just followed which was on air.

The main Teletext Ltd service didn't care which company was on air as it was added right at the last point of the TX chain