Many of their routes are very easily done by train -- Birmingham to Glasgow, London to Exeter, London to Newquay, London to Newcastle.
Faster trains would make more places in Scotland a reasonable travel time away from London and Birmingham.
Southampton to Leeds, Manchester to Cornwall, and of course Belfast to anywhere isn’t easy or fast by train
We’re now trying to catch up with HS2, which is sorely needed to free existing tracks for more and reliable services, but we need to use that as a springboard for 50 years of investment. HS2, npr, midland connect, then high speed Birmingham to Bristol/Cardiff, Cambridge, and Leeds-Newcastle-Edinburgh-Glasgow
The key is to ensure we have schemes ready to go once construction winds up on the first parts, so the skills and equipment aren’t lost.
I don't like checking luggage on planes for various reasons but the system is at least set up to accommodate it straightforwardly.
e.g. Cambridge to Edinburgh (I haven't checked the connection time for this).
If when California finishes it's high speed rail line all they need to do for it to be a success is keep the TSA far far away from it.