How would Britain's railways have developed if ...

[Harlesden]

... the postwar government had been a Conservative government firmly against nationalization?

 

[ACE1888]

Well the way BOTH the main Parties treated our rail system in the 1960's answers it's own question. When you're 'in the pockets' of the Road Lobby, it was always going to happen sooner rather than later, congestion/fuel prices were probably not even thought of back then?
However...perhaps WITHOUT 'British Railways' with 'Regional' knowledge, the changes would probably been far less severe, one for the 'Historians' to debate I'd say...

 

[Schnellzug]

Ah, fantasy Railways, one of my favourite fields for speculation. Well, if we leave aside pure political dogma (" It's a process of historical inevitability that they would be taken into state ownership!"), I wonder how the Great Western's experiments with Gas Turbines, and the plans for Electrification, might have developed...? And what about the LMS diesels, how would they have developed? And what about the steam designs that were on the drawing board; the 4-8-4 'Super Duchess' and so forth? Would Bulleid have managed to get the Leaders working properly?
One thing, I think, you can bet; that the companies would have pursued a more rational programme of replacement; they wouldn't have built hundreds of steam locos and then begun to replace them after five years, with a vast selection of diesels that didn't last much longer than about 10 years themselves.