Many thanks Savemoney. This is yet another example of how useful this forum can be, not only for expressing opinions but also for money saving tips like these. It’s probably not much use to UK residents but I see plenty of forum posters live outside the UK and for us it is a boon.
I was about to rent a car to take the family to Cornwall after I saw the 1st class train prices. But this pass makes it very economical, consequently I have just ordered them. On top of it all, my children will travel free!