Not me saying this (although I agree with the argument) but a former boss of the Strategic Rail Authority:
“On regeneration, I know of no serious academics who support the view HSR will significantly reduce the North-South divide. Most research indicates the dominant ‘hub’ city benefits more than regional centres and in the regions the impact is likely to be a zero sum game.
“A Leeds HSR station would probably be surrounded by shiny new office blocks, but investment in West Yorkshire would be focused there, and the relative decline of Bradford would accelerate.”
And that's before all the suits whizz off to London on the lovely fast train we've built for their convenience!