It is easy to point the finger at Beeching, though he was given permission to look at wholesale decimation in order to try and reach the holy grail of profitablility. Some closures he proposed were never progressed while others he did not recommend were progressed at a later date. Having said that, the Freightliner concept, the InterCity business and eventually the HST125 all had their roots in his recommendations. The mendacity of Marples cannot be ignored though, holding an interest in a road construction business while overseeing the railways is a putrid piece of British political history.
However, railway closures had been going on for a considerable time. However, prior to the grouping in 1923 they were often small in scale, down to alterations in routes, either due to new building drawing away traffic, new technology drawing traffic away from the line or the failure of the industry which had provided the impetus for initial construction. Colliery railways had faced the first and third threats almost since their inception, while the N.E.R. faced the second threat post-1900 on Tyneside with the rise of the electric tram and they countered it by electrifying the lines to North Tyneside.
The L.N.E.R. faced the second threat right from the start, with motor omnibuses literally exploding post-WWI while drawing on a supply of vehicles and ex-military trained drivers. The motor wagon drawing off goods traffic seems to have not exploded in the same manner until post-WWII, with the same impetus of surplus military vehicles and ex-military drivers. The passenger service to Dunston fell to buses as early as 1926, with a glut of passenger closures around 1930 (Amble being an example where bus services could match the time of the train to Morpeth while beating it on price and frequency). More passenger services went in 1939, with the Lanchester valley branch being an example there, though passenger traffic had been falling relentlessly since 1921. Despite the village centre location of Lanchester station and the proximity of Witton Gilbert station to Langley Park the passenger train service frequency was low and Blackhill station was not as attractive a destination for shopping or business as Consett, which was reached directly by the frequent bus services. A change of train was necessary at Blackhill in order to reach Consett station (or a mile long walk up a steep hill), but the change meant that the journey time from Lanchester was hopelessly uncompetitive compared to the bus.
British Railways picked up a poisoned chalice upon nationalisation. There never was enough government money, the railway companies had seen their equipment run down again during wartime with the government short-changing them on the funds to make good the depreciation. Some rural services would have been cheaper to run by operating a taxi from the junction station to the branch destinations! British Railways were not without sin though. If they wanted a line to close one option was to provide an abysmal timetable (missed connections, unattractive times) and then say that there was no demand for the trains. Rural lines were the usual target but if your main line was a duplicate of one built by a bigger pre-nationalisation competitor then there'd likley be some shenanigans in the chase for substantial savings. Examples were delivering the G.C.R. London Extension to the London Midland Region and the L.S.W.R. main line west of Exeter to the Western. The Midland main line to Manchester was culled beyond Matlock and gradually strangled beyond Leeds to Carlisle. Closure of the Settle & Carlisle was missed by a whisker in the mid-1980s and that was partially down to some "counter-shenanigans" by the district manager! The Waverley route in Scotland did not have a similar manager in place in the late 1960s.
Trains will probably never return to the woodhead route since the new tunnel now carries a 25KV power line and there appears to be no political will to take the rebuild of the Exeter - Plymouth line via Tavistock, despite the "money no object" promise in the aftermath of the Dawlish troubles. The East-West Rail project between Oxford and Cambridge has been derided after the government de-specified electrification. As usual, the treasury will grasp with both hands the idea of saving a pouind now, even when acknowledging the five pound cost of dealing with the consequences of their saving down the line. Once again, the training and skills gained by the latest crop of electrification engineers since 2010 will be allowed to drain away and force, for the fourth time since 1970, the business to start from scratch and relearn the consequences of mistakes the hard way. I could go on but it will bust the character limits.