In fact, the railway network began to shrink in the 30's, particularly narrow guage lines such as the Lynton & Barnstaple, Leek & Manifold, Glyn Valley were early victims, being unable to compete with bus and lorry, while others such as the Corris and Welshpool & Llanfair continued as freight only.
Outbreak of war stopped further retraction, the railways were in fact nationalised in all but name, this being official in 1948. Postwar attitude was different. The public looked to the freedom of the open road, new (now regarded as classic) sports cars, the new London - Birmingham motorway. In contrast, the railways were seen as slow and dirty - this epitaph was applied to the Somerset and Dorset -S&D. Grimy steam locomotives hauling grimy coaches crewed by grimy men puffing slowly around hill and dale, always late, was the public perception.
Road public transport took a battering as well. By the early 60's only Blackpool had a street tramway, the trolleybus would be extinct on British roads by the early 70's. London busmen went on strike for 6 weeks in 1958, when London started to replace its trolleybuses, there were enough surplus RT buses from reduced demand for the first two stages of trolleybus replacement.
The railway network was still shrinking. For example, the Isle of Wight lost lines to Freshwater, Bembridge and Ventnor West in the early 50's, Newport - Merstone - Sandown mid 50's
The railways responded by the 1955 Modernisation plan, part of which wasted money on unreliable diesels - two of these ended up in Barry scrapyard alongside the steam locos they were supposed to replace. When the Treasury saw the sums involved, it panicked - the taxpayer would never stand for this. The railways responded by asking to be put on a commercial basis, so in 1962 out went the British Transport Commission and its obligation to be a common carrier and in came the British Railways Board, and Beeching was brought in - an accountant with ICI, to carry out a survey of the profitability of the system. Lines and stations were graded, so there could be a point at which a line could be drawn, everything below that was unprofitable and earmarked for closure. When the Beeching report came out, most went straight to the dreaded Appendix 2 listing lines and stations recommended for closure.
One wonders what the preservation movement would be today if history took a different course, as it was this mass slaughter of lines and steam locomotives which catalysed it. Formerly, the railways scrapped their own locomotives, they only turned to outside agents during the final years of steam being overwhelmed by the sheer volume of engines to be scrapped. If there was no Barry, would there only be 2 Bullied Pacifics preserved - Winston Churchill and Clan line?
Again a trickle of closures continued post Beeching. In the West country, Okehampton - Bere Alston went 1968, Ilfracombe 1970, was Bridport around 1976? and freight only to Meeth 1982.
The 1970's were bad for the new look British Rail despite hiring Sir Jimmy Saville to remind us that this was the age of the train. British Rail was standard fare for comedians regarding unpunctualty and unreliability. I am reminded of Old Timer's post, that it made news when ASLEF refused to move coal by rail while the miners were on strike, and it was found that it was cheaper to use road lorries, this traffic was lost to the railways forever.
As for the Somerset & Dorset, proposals for a new diversion and terminus at the Bath end of the line were proposed, but again defeated by cost. The desire was to haul the Pines express by diesel, the S&D infrastructure was not up the the heavier demands of diesel traction, so the Pines was diverted off the S&D, went diesel and the S&D remained a steam branch until closure