OK, that puts a rather different complexion on it.
> To me, it's not clear that a return to a nationalised operator would help things in GB; ... the railway is far more micromanaged by the government today than it ever was under British Rail
True, whilst I understand the reasoning of Labour's suggestion to re-nationalise, at best we would get a less effective repeat of 1947. 1947-1960 (before Beeching) worked OK in good part because BR still had the shape of the big 4 years. Even if Labour planned, executed and funded perfectly we would, at some point, get a Tory government, who would be inclined to under-fund it. Off we go again, still with infrastructure 50 years behind.
I mention nationalisation more as a reason to bring it all back into one whole first -- to split it up more sensibly at the next attempt. Divvying up various bits of all the various companies differently seems challenging. :)
The central micromanagement speaks to other UK post-war problems, which also affect rail. We've become one of the most centralised countries there is, whilst talking of smaller government and deregulation. Local funding has been steadily gutted since the end of the general rates. Local authorities used to be able to make far wider reaching decisions, and fund them. They could start, fund or develop local services, such as bus, power or train, and often create a municipal corporation to run it -- hands off.
That's the other appeal of returning to the pre-war organisation, it would distance the government from the day to day, and local choices, especially in Scotland, the North etc, might be possible once again. We could add capacity, and undo some of the worst of Beeching.
Now if only we could only undo some of the UK's excess centralisation as well...