Anyone know what will happen to BBC when it goes HD only on the Irish Sky+HD box?

Not a stupid decision at all. Recent reports in the UK media press suggest that 98% of UK viewers receiving broadcast stations via satellite are using equipment capable of receiving HD broadcasts from the BBC, ITV, Ch4 & Ch5, and that the BBC are bringing forward their SD "nightlight" shutdown forward by 2-3 months as far fewer potentially affected viewers have been contancting them for help on it. There's pretty much no justification for the Beeb to keep SD broadcasts going for a very small amount of viewers whom have been advised well in advance of the upcoming SD closedown.

ITV are also taking the opportunity in the next couple of months to finally start broadcasting the Border Scotland and Channel Isles regions on satellite at the expense of their corresponding SD broadcasts (a short simulcast will exist) which will also see UTV's SD broadcast end on satellite too in January. Outside of STV land, that'll leave just four ITV regions on SD on satellite - in Scotland (outside of the Border Scotland region) the four STV regions will remain in SD for now, only the STV West region is FTA in HD, the other three are FTV.

Aside from these, other SD simulcasts of HD broadcasts have been gradually stopping as fewer viewers are using SD only receiving equipment - quite recently Sky's rebrand of Pick to Sky Mix seen it 'launch' in HD with the SD versions being turned off a few days later (then brought back on again, before being turned off for presumably good), while CNBC has also recently terminated its SD channel on Astra 2, leaving just the HD broadcast in its place.

Anyone who is still relying on old satellite reception equipment for watching FTA broadcasts from the Astra 2 satellites really need to start changing IMO - it's only a matter of time when ITV will go HD only themselves, as will the main Channel 4 & Channel 5 stations themselves (the other channels that they run OTOH are subject to additional factors).

As to the OP's initial issue - the caption being broadcast is intended for a domestic UK audience. ROI Sky subscribers watching or listening to BBC broadcasts are watching the same video & audio streams as UK viewers are. Ultimately, viewers in the Republic that are seeing these captions on the main BBC stations in their EPG (excluding those in the 800 range) should contact Sky Ireland as they'll likely need their viewing equipment upgraded.

HDTV has been a continous term and cycle of upgrades that has been going on for a almost a century , the newer system being called HD and the older system being called SD until it becomes obsolete and the newer system gets the SD tag .......

From the wiki .....

https://en.wikipedia.org/wiki/High-definition_television

" The term high definition once described a series of television systems first announced in 1933[1] and launched starting in August 1936;[5] however, these systems were only high definition when compared to earlier systems that were based on mechanical systems with as few as 30 lines of resolution. The ongoing competition between companies and nations to create true "HDTV" spanned the entire 20th century, as each new system became higher definition than the last. In the early 21st century, this race has continued with 4K, 5K and 8K systems.

The British high-definition TV service started trials in August 1936 and a regular service on 2 November 1936 using both the (mechanical) Baird 240 line sequential scan (later to be inaccurately rechristened 'progressive') and the (electronic) Marconi-EMI 405 line interlaced systems. The Baird system was discontinued in February 1937.[6] In 1938 France followed with its own 441-line system, variants of which were also used by a number of other countries. The US NTSC 525-line system joined in 1941. In 1949 France introduced an even higher-resolution standard at 819 lines, a system that should have been high definition even by today's[when?] standards, but was monochrome only and the technical limitations of the time prevented it from achieving the definition of which it should have been capable."

SD today , something like 720 x 576 ( it varies , some sat channels are lower ) is being phased out as obsolete and the new SD is now 1920 x 1080p , the new HD being 3840 x 2160p

Most new content on streaming services is now 3840 x 2160p with some form of HDR and Surround sound format like atmos.

Figures would suggest that is how most people are watching , streaming in UHD/or 4K .

Watching Planet Earth III in 1080p on BBC is very poor compared to the UHD version available.

Technology marches on , as always ....

Agreed , watch pointless on challenge vs pointless on BBC1 HD , and if you cannot see the difference its time for an eye test.

Ive got a 22 inch Samsung 1080p LCD TV in the Kitchen , and when watching Saorview , there is a very noticeable drop in quality from RTE 1 &2 in HD to say RTE News and any of the Virgin Channels in SD.

SD channels can vary in quality greatly , compare say , Challenge or Yesterday to Dave ..... big jump in quality there.

On the Subject of Virgin , their HD service is truly brutal , Ive got a 360 box and their Cable Service because there was no price difference between Gigabit broadband with or without TV , so can compare both it and satellite ( VU+ Enigma 2 box running Openvix ) and the quality drop between the same HD channels on both is marked. Virgin is very poor , for what reason I dont know , low bitrate maybe but it is really bad.

So maybe the above posters that cannot see the difference are on Virgin TV.

I'll miss the SD BBC channels. Would switch over around the 9/10pm time slot when the local norn iron programming came on. Much rather Detectorists or Upstart Crow than Barra Goes for a Walk.

Yup , agreed , ITV 2 ,3,4 sometimes very poor indeed , ITV 1 seems to be fine most of the time though. Myself , I cannot stand ads , so if there is something on there I want to watch it gets recorded so I can skip through em.

Otherwise everything I watch is streamed in UHD with HDR , now HDR is something else ..... the jump from 1080p to 2160p would never have flown if HDR hadnt been thrown into the mix.

HDR is something you really do need a good screen for , the cheaper LCDs dont get the benefit of it at all.

I got an LG CX a couple of years ago , now that is jaw dropping with HDR ..... first thing I got was a box set of Planet Earth II and Blue Planet in UHD HDR ....... WOW !! and that was coming from a Panasonic Plasma , which was the best at the time it was bought .... old hat now though.

This is incorrect. The difference between HD and SD is stark and anyone that cannot see it either has their equipment setup incorrectly or has eyesight problems.

Don't want to lose all the great channels I have or give sky anymore money..! ah it'll be grand as its only bbc1 can record on sky q if its something important. Only reason I stay with sky is because of record function.