Just in general about BR, is what I mean
There were at least 5 versions of BR as the organisation evolved.
Initially (1948) all transport was nationalised, including road (most buses and heavy lorries), canals and air services, as well as rail.
All the other modes were re-privatised subsequently, and even BR was stripped of its hotels, ferries and eventually rolling stock manufacturing which were all sold off.
Much railway land was sold for development, including some very large sites in London.
There was always some competitive private manufacturing, mostly locos, as well, which mostly ended up in GEC (which later became Alstom).
There were also Pullman passenger services with a private interest for some of the time.
Just before privatisation, BR was split into infrastructure (Railtrack) and operations (BR sectors) which were then privatised/franchised.
There were a host of support functions which were also sold off (research, testing, maintenance, international etc).
The franchises were only a fraction of the totality of BR.
Most of BR was organised into Regions which were the successors of the Big 4 companies. They were pretty autonomous and did things they way they always had been done.
It took BR a long time to centralise the decision making into one network.
The business sectors (Intercity, NSE, Regional, and the freight sectors) started around 1980 but were initially only marketing teams, with services supplied by the Regions.
In 1993 the Regions were finally abolished and split between the Sectors, but that model didn't have a chance to prove its worth as it was overtaken by privatisation.
A good description of how all this evolved in the early years is in "The Train That Ran Away" by Stewart Joy, a former member of the BRB.
It's worth remembering that in its 180 year existence the railway was in public hands for just 50 years, while prior to that was in private hands for 100+ years.
I'd just say that the Beeching years marked the point when BR lost control of its finances, and since then has always been closely managed by the Treasury.