I'm not sure HS2 is the best example. I'd have preferred to see the money spread around the network so everybody benefits.
More or less everyone does benefit from HS2, because the segregation of express services off the legacy network has profound impacts on the national network. Basically, mixed-speed traffic is very inefficient - same reason why buses and bicycles aren't allowed on motorways. They're dedicated as express routes.
The moment Curzon Street removes all the Glasgow/Manchester-bound trains from New Street, the capacity for West Mids stopping services, as well as trains down to Bristol/Cardiff/Exeter quadruples. A nationally-significant bottleneck around Birmingham/Coventry is released.
If HS2 is built in full (to Leeds), then you provide the same capacity release on ECML and MML. The East coast in particular needs the fast trains gone to make space for rail freight from all our east-coast ports, which the likes of Amazon and Tesco are investing heavily to get HGVs off the road (slow, get stuck in traffic, need lots of drivers).
HS2 is a 3-in-1 upgrade to our major Mainlines. You could achieve the same by putting in a 100-mph "express" line for non-stop services parallel to each of those lines - traffic segregation is the aim, not outright speed. But that would cost a great deal more than building one 200mph line (which also, as an additional benefit, starts to undermine domestic aviation like London-Manchester).
Biting the hand that feeds IT
