however the newer ones are significantly better
funding the capital cost of a billion pounds of new trains isn't free (even for a government), and there is risk on that investment
they also maintain the trains (to varying levels of quality)
Is this sarcasm that I am missing? There is absolutely no reason that Government (or a Government-owned business) couldn't "afford" rolling stock. That's a really poor excuse (and completely made up) if they claim that.
This annoys the hell out of future governments, because it's effectively tying their hands, but it also lets the current government look like it's doing a lot more in its short term without raising taxes.
There is nothing that the private sector can afford in the UK that the UK Government can not afford!
- Network Rail, who maintain the entire country's track, signalling, etc. Also owns and runs some major stations. Run at arms length by government, centrally funded.
- Train Operating Companies (TOCs), who won a bid held every few years on how much they'll pay the government to be allowed a monopoly on running a particular regional service franchise. Government sets the rules of the franchise, e.g. customer compensation, punctuality targets, etc. TOCs have no control over the network. They lease trains from ROSCOs. They pay and schedule drivers, guards/ticket inspectors, ticket desks, customer support, station staff (they're also responsible for running most stations), and get money in by selling tickets to the public.
- Rolling Stock Companies (ROSCOs), who own (commission and maintain) the trains and lease them out to TOCs for exhorbitant prices. ROSCOs extract most of the value of the railway. ROSCOs exist because trains are so expensive that neither government nor TOCs can afford them.
Many of these TOCs are other countries national rail operators in disguise, e.g. the Scotrail franchise was recently run by Abellio which was actually the Dutch national railway company (NS). So all profits (not that there are many) leave the country and subsidise other countries' rail networks.
The current government has committed to taking back ownership of all TOCs at the end of their franchise terms, so in future both Network Rail and all TOCs will be publicly owned.
But at the same time, that might not make anything cheaper; most of the value is sucked out by ROSCOs, so unless the government commits to buying its own trains too, the ROSCOs will just charge more for the same trains if they see the government finding any efficiencies, ensuring tickets don't get cheaper.
Some fuming about ROSCO dividend payments: https://www.rmt.org.uk/news/rail-rolling-stock-company-turns...
And to add to that, much of the cost (or cost savings) the TOCs were pursuing were effectively industrial relations - can they get away with having driver-only or driverless trains, in order to have just 1 or 0 paid staff member per train? Unions say "no". Union members start working to rule and suddenly you have no trains on Sunday, even if you're the government.
So... it's tricky.