It's fascinating what might have been built. WW2 changed a lot of things, including the fact that I would have been a lot older if my father had not been away serving in the army for king and country.
The biggest problem for me was that railways had come under Government control and this led on to the closure of much of the system (thanks to arch-villain Marples & his sidekick Beeching) for political/greed reasons. This followed on from the fact that the railways, having served faithfully throughout the war, were short-changed by the Government and then found themselves strapped for cash. So the Attlee government said "never mind, we'll take you over and all your problems are over!"
The railway's worst problems were that the Min of Transport (MoT) were repeatedly favouring road improvement schemes rather than rail schemes and the MoT carried on doing everything they could to close the system down.
Well that worked well. We now have a ruined road system because all the heavy freight is moved by lorries which have battered our roads into a mass of potholes. And the lorries aren't even British! Think Iveco, Renault, Mercedes, MAN, Volvo, Daf.
I could go on, but I won't.