[Bluecortina]

This one here, from the Saturday morning kids show "Motormouth", is interesting. Three things make it interesting. Firstly, it's a TVS show, so is therefore TVS networking it, but secondly, the colour bars are from HTV, no idea if Bristol or Cardiff, and lastly, this recording is from the LWT region. How did it end up with HTV colour bars, on LWT on a TVS show?
www.youtube.com 

It could be that it was just an accidental switch of the BT circuit into LWT (and possibly everyone else) - so suddenly the one from Maidstone becomes one from Cardiff or Bristol.

Alternatively, it was a mistake in LWTs lines room. Someone routing another incoming circuit (or a VT that just so happened to have HTV bars on it) onto the OS line into the TX suite that had Motormouth on it. The fact it was a clean sync cut between the two and it was resolved fairly quickly make this seem the more likely scenario

All main incoming circuits to the South Bank had synchronisers on them so a clean cut between the two different external sources would not in itself mean too much I think. The short period of black between the two sources however would indicate to me a synchroniser sensing a momentary loss of incoming signal and outputting black (a standard synchroniser’s user setting) and then reinstating the output once the next stable source came along - whatever it was. 

I would guess Maidstone into SB via BT tower for networking via LWT (TVS being the originating company). I would have to consult my old IBA routing maps but I’m pretty confident Bristol was direct to BT tower and unless a Bristol circuit was required at SB on a Saturday morning perhaps we would be looking at a BT tower switching error? The length of the ‘fault’ would seem typical of a switching fault, SB immediately noticing, buzzing BT to tell them of the error and BT correcting it.

But of course as is so often the case we will never know.

PS. Circuits into SB were known by their individual KRS numbers, these were then assigned as ‘Remotes’ (Rem 1,2 or 3 etc) for internal distribution around the technical areas, ‘OS’ was not terminology used by LWT although I understand why you have used it - I only mention it just for info.