I don't think Marples was a villain either. Just because he was a significant shareholder in a civil engineering company didn't mean he was pro-roads either; civils companies build railways and non-transport structures just as much. And Britain was doing no more than all other principal countries, rebuilding their roads structure as road vehicles had rapidly developed to become a very mainstream transport medium.
However, the government was seriously hacked at the inability of the rail industry to advance, instead of sticking with the approaches of past generations, at the considerable amount of the system serving little or no useful purpose, and the poor investment decisions such as the modernisation plan that, while some was straightforward, had also spent considerable amounts of capital on nonsense schemes. You don't even have to read Beeching - Gerry Fiennes' books have plenty of examples of this squandering of resources. Fiennes, Beeching, and the others of their generation could all see it, but were swamped by traditional inertia. You only have to look at the overbuilding of the initial stages of the WCML electrification, wiring every road in yards where all the work was done by diesel shunters, and many other similar aspects.
Marples signed off a lot of expenditure for proper Inter-City stock, Diesels that finally worked and had sufficient power, Merry-go-Round coal, the first Freightliners, cwr, power signalling, and such like. The railways were not generating any cash of their own - that was all government money. All the revenue was pretty much spent on half a million staff.