So... brfares.com lists
CIV▸ fares for e.g. London International - similar to standard single/return off peak + peak prices.
Also to various destinations on the island of Ireland, in which case prices and conditions are more attractive.
There must be a book to be written on 'Great vanished routes that at one time had through ticketing via rail and ship'...
Here's Bristol to London International (CIV)
https://www.brfares.com/!expert?orig=bri&dest=LNE
Rail Europe has a helpful explainer. At least, I hope it's helpful.
https://help.raileurope.co.uk/article/41665-understanding-civWhat, though, is the Euro
Apex▸ CIV? Info from National Rail
https://www.nationalrail.co.uk/times_fares/ticket_types/EAS.aspxOverall tl:dr - even with CIV, consider quality travel insurance that covers expenses consequential to missed connections.
Is there a chapter to be written on how the rail industry can best handle this with an eye to growth? Goodwill goes a long way, but for all those people buying advance tickets as part of an onward journey involving international travel by all modes, there's a mismatch between the tickets offered by the rail companies versus what may be asked of them and perhaps there's a way to address this. The whole 'Onward travel by rail or air' experience shouldn't rely on having to make distress purchases when things go wrong.
Mark