I think nationalisation is by far the best way to run the railways since the majority of lines are loss-making, but also provide a crucial service to society as a whole and permit a lot of people to travel who otherwise wouldn't be able to - however, under this current right-wing government, and even under a centralised government if they get into power soon, this will never work, as everyone is way to focused on reducing costs and no one actually sees the societal benefits. Only a left-wing government would be able to properly support the railways and allow them to grow in a way that supports all the people in the country.
Now the truly controversial part - I think a lot of rail enthusiasts are quite right-wing in their political views (as I would expect since there are a lot of enthusiasts who are old white men), but supporting a train system as vast as the UK's is quite a left-wing view. This, therefore, causes confusion and they try to justify right-wing policies such as more extreme privatisation by claiming that it would work on the mainlines, but deep down they know that it would kill off most of the railways in the country.