I've travelled on UK railways extensively, and on many main lines there is spare capacity where four tracks were reduced to two, or two reduced to one in the sixties.
I can already get to London in two hours from Yorkshire so to me, HS2 is tragic misuse of funding. That money should be spent on reinstating four tracks, and reopening closed lines where the demand is there.
Our Pacer units are the worst in the country. Commuters face serious overcrowding every day, but its better and faster than driving in to work.