On an island the size of Great Britain there should be little need for air services
I think you should consider what the meaning of "island" is.
if we had an effective high speed rail system. Rail can provide city centre to city centre services. If we had a rail system like Japan's Shinkansen we wouldn't bother flying.
Well we can't have an effective high speed rail system, at least not at any reasonable price.
To travel from the centre of, say, Glasgow by air you have to travel to the airport to arrive at least an hour before you flight time and you will spend about 30 minutes getting off the plane, collecting luggage and getting out of the terminal ... and then spend another hour getting to the City or the West End.
Heathrow to Paddington on the Heathrow Express takes 15 minutes.
A flight time of an hour or so has been supplemented by between three or four hours. A HST would have taken less than three hours - seated and possibly working.
Your flight time is nonsense. You can arrive at Glasgow airport an hour before the flight and still make the flight (it's domestic) and, with hand luggage only, you can be outside the terminal 15 minutes after you land. It's then 15 minutes to Paddington. central Glasgow to central London is achievable in three hours by air. Furthermore, for anybody coming from West of London to Heathrow, Heathrow is more convenient than a railway station in the middle of London.
Incidentally, the people objecting to the potential destruction of historic woodland by HS2 should consider the fact that the completed railway from London to Birmingham will take up much less land than does Heathrow Airport.
Yes, but Heathrow is already there. Also, if you are trying to get to Glasgow, a train that goes as far as Birmingham is not of much use.
Also, the difference is marginal. It's approximately 600 km (less as the crow flies but we need some literal wiggle room) from Glasgow to London. Heathrow is 12km
2 which means that if you stretched Heathrow out to 600km long, it would be 20 metres wide.
I just measured the width of the track of HS1 just south of Ashford International and it's 16 metres. But we haven't yet taken into account the space required for cuttings and embankments, or new stations or new buildings required for the displaced occupants of buildings demolished to get the line into London and Glasgow and through Birmingham and Manchester (I assume you want the trains to stop there too).
Sorry to post such a downer. I love trains and I'd much rather travel to Glasgow on one than in a plane, but we do need to be realistic about the options.