The Grouping was a government led amalgamation of four large Railway Companies from dozens of smaller companies, many resisted but government had its way and the “Big Four” came about in 1923.
Amongst the constituents of the LMS was the Midland and its bitter rival the LNWR.
The LNER absorbed the Great Central, Great Eastern,Great Northern and North Eastern Railway.,
The Southern took over the LBSCR, LSWR and SECR.
However the strangest fact of all was that the Great Western only absorbed minor railways and in so doing remained pretty much as it had always been.