1948 BR was formed from the Big Four [1] but they themselves were formed from the merging of many smaller operators over the preceding 50 years or so (if I remember correctly)

TBH BR performed reasonably well given investment until they were sold off into the private sector where productivity of staff and reliability slowly started to decline. This was matched be an increase in use so it's hard to see if the sell off caused the problems.

In the 1970's BR designed and prototyped a high speed leaning train but government funding was withdrawn because of fears that 'britain can't manufacture anymore'. The start of the end IMHO.

[1] - http://en.wikipedia.org/wiki/Big_Four_British_railway_compan...