There is no public appetite in the UK for more rail capacity, or for faster services, so the only way to control numbers and prevent people from being (mostly) left behind is to increase costs on the busiest services.
This is fortunate too, the UK does not want to subsidise rail to the same extent as france -- Rail subsidies per passenger km (in euro-cents)
Netherlands: 14.7
France: 15.7
Italy: 19.1
Germany: 21.4
The UK in comparison is 6.75.
UK: €64
France: €203
Germany: €209
The UK makes a conscious decision not to subsidise its rail network to the extent of France and Germany. I'd rather we had spent the last 40 years building high speed lines, but as a country we didn't want that.
My list would be
* HS2 as now planned, extended up the east coast to Edinburgh, Glasgow and Aberdeen
* Plymouth -> Exeter -> Bristol -> Birmingham -> Cambridge -> Norwich
* Swansea->Cardiff->Bristol->London
* Liverpool-Manchester-Leeds-Hull
With junctions to allow services to run as appropriate for demand (e.g. Swansea-Cardiff-Bristol-Birmingham once an hour, continuing to Manchester or Leeds, Swansea-Cardiff-Bristol-London twice an hour, Liverpool-Manchester-Leeds-Newcastle-Edinburgh, etc)
Had we done that we'd have the capacity to offer cut price, but alas we didn't.
As it stands, trains - especially cross country ones - are massively crowded even with the price as high as it is, because people prefer to take a dog-slow overcrowded train from Reading to Manchester, rather than to take a cheaper coach.
The problem with the UK is that if you compare HS2 to comparable French lines, we are 10 times less efficient at procuring public projects than they are. They can cross the Massif Central for ~€30m/mile, we cross the Midlands for ~€300m/mile. In flat country their costs are much lower, Paris-Bordeaux cost ~€10m/mile.