I'm so glad I asked about this issue on here. The number and variety of answers has been much higher than ever expected and have been gratefully received.
Given that the journey is tomorrow and it's expected to be hotter than today, I suspect fares/tickets may be the least of my son's challenges tomorrow.
By the way, every time someone explains "routing points" and "easments" and "maps", I always think of the game of "Mornington Crescent" on the BBC Radio 4 show I'm Sorry, I Haven't a Clue----- More info here:
https://en.wikipedia.org/wiki/Mornington_Crescent_(game).
Is it just me?