This is a non-starter, the tracks in the uUK cannot support high speed trains without extensive re-newal, the Infrastructure is not in place for the added passenger loads and digitalsi got it spot on, errr, 100yr old tunnels and bridges designed in the Steam Locomotion age are not going to allow double decker trains, and replacing these all would bankrupt the country!
80 yrs on and it still takes the same time from London to Edinburgh on the train! ITS A BLOODY MESS!
And the Interior would not work, needs to be vandal proof!