ITV Channel Islands HD

That happens all over the UK though as not all regions are in HD or have a +1 so there are many places where local advertising is only going out on ITV SD.

Aren't all the regions HD now? I'm sure they did that a few months back, certainly Central East went HD recently.

Only two (on satellite) not HD now Channel, (as discussed) and Border-Scotland

Still quite a few missing on Freeview

Only on satellite (with the exception of Channel). Freeview still has the old regional ITVHD set up so many viewers are still receiving the wrong region in HD. I think ITV+1 also now has fewer regions than it did before October.

It only actually carries ITV London HD (It's listed as Central on KingofSat but last time I checked it was definitely the London version). STV HD and UTV HD have no video or audio data, but I'm fairly sure I remember there being an MHEG stream for each, which I would guess might be a "sorry this service is off air" kind of caption for any transmitter that ends up taking the feed.

The BBC One SD (England) version on there is a special "region-less" one that carries the BBC News Sportsday bulletin at 6:30pm where the regional news would go. BBC One HD is the normal English version with the red "switch to 1/101" caption.

As you say, the SI for all regions is carried on there, which must get filtered and assembled at any transmitter using the feed. There's EIT ( EPG) data on there too, on a non-standard PID (58 ). I've only seen present and following information on there (now and next) rather than the full 8 day extended EPG, but it might be being transmitted!

Cable too, as that's how we get it. ITV HD moved from 113 to 103 once Central East HD launched.

Does it carry the News Channel at 1330 and 1830 too? If so that's BBC One network sustaining (that BBC One HD England opts out of to carry the red slate and preview barker)

Yes, same here recently. Used to get Meridian SE on Satellite and Freeview, but now we get (correctly) the Thames Valley flavour of Meridian South on satellite.
Freeview is still Meridian SE
Confuses Mrs MM with the GMB opts when she moves between the bedroom (Freeview) and the living room (Sky)!

I'm fairly sure I've seen it do so at 13:30 too - I will check again!

The HD channels on Intelsat 901 are as they would be usually via terrestrial, but the BBC One SD versions are all CBR (the same bitrate for each one), so that the correct version can be combined with the other (stat-muxed) BBC SD channels on there at a transmitter in any of the four nations. A bit like how the first BBC One opt-outs worked on DTT.

As only BBC One SD is (loosely) regionalised, you can see in the transmitter engineering updates when a site has fallen back to this feed as it's reported as an "incorrect region" fault.

Kind of getting off topic but I've heard mixed things about 'international' BBC One as carried on Zattoo, etc. Is it the sustaining Sportsday feed, the HD feed or London?

The Swiss providers take BBC One HD (England) from 28E. It used to be BBC One London SD. ITV HD is from London, so you can watch ITV News London in Geneva or Zurich.

As far as I know, it's BBC One HD (England)/BBC One London SD/BBC Two England (SD/HD) on Belgian and Dutch cable, most likely from satellite.

In the Netherlands, I'm fairly sure they downlink off 28.2°E as their feed for BBC One and BBC Two in SD at least. For the Ziggo cable network, this multiplex scan suggests it's being passed through without the video/audio being re-encoded -https://www.digitalbitrate.com/dtv.php?mux=C049&liste=1&live=202&lang=en

For HD, in Belgium/Netherlands it's probably the same, although multiplex scans of both Voo (Wallonia) - https://www.digitalbitrate.com/dtv.php?mux=C029&liste=1&live=203&lang=en - and Ziggo (NL) - https://www.digitalbitrate.com/dtv.php?mux=C022&liste=1&live=202&lang=en - show BBC One HD as being stat-muxed with other services, so if they're using the satellite version then they're re-encoding the video at least, although the audio at 192/384kbps AC3 hints at a passthrough of the satellite encoding. Having said that, they may be getting a fibre feed along with the BBC Worldwide BBC First HD channel they get in these countries. I’d still be surprised if it wasn’t just BBC One HD with the red screen though.