The nationalised UK railways
system, in place between 1949 and 1997.
When the railways were nationalised in 1949 they were suffering from a lack of investment and a backlog of routine maintenance caused by the disruption of the Second World War.
When the railways were privatised in 1996 they were suffering from a lack of investment and a backlog of routine maintenance caused by BR.
British Rail did do a lot to modernise the railways from what they were before, which included closing many stations and lines. Fairly high speed (though often unreliable) services were introduced between major cities, and many commuter services were brought into urban areas with the formation of local Passenger Transport Authorities.
In the late 80's/early 90's, the company was split into business units (such as InterCity, Regional Railways and Railfreight Distribution. This seemed to make life easier when it came to privatisation, when 35 Train Operating Companies took over, and Railtrack assumed ownership of the lines and major stations.
The companies which took over from BR can be found in the Train Operating Company meta-node.
Sources: Railtrack and www.rail.co.uk