Probably the cheapest and best option is to build more wind and not care too much if it increases curtailment.
Yes, all the things mentioned should be looked into and done when it makes financial sense but "wasting wind" is much less a thing to worry about than "burning gas", and I'd rather waste wind than waste money.
Maybe not: "The Transport Secretary announced on 19 October 2022 that the Transport Bill which would have set up GBR would not go ahead in the current parliamentary session."
Network Rail sells access to the network to train operating companies, which are private (though often state-owned by other countries).
The network was originally built by private companies until nationalisation in 1947 (railway companies were bankrupt after WW2). It was private for a while in the 90s, then went bankrupt and renationalised in 2002. Seems to be quite the money pit!