This information is extracted from 2 books by M. D. Beckett and P.R. Hemel. The books are called M & GN in Action and M & GN in Focus.
Introduction – With its King’s Lynn headquarters, its Melton Constable locomotive works, its beautiful golden gorse loco livery and its glorious mixture of second-hand rolling stock proudly lettered M&GJV, Britain’s largest joint railway had its own air of independence, particularly during the long guardianship of Engineer and Traffic Manager William Marriott, the man who caused Melton Works to produce sixteen locos to its own designs!
Yet the line was jointly owned: by two railways—the Great Northern and the Midland—which had not always seen eye-to-eye. Formed to break the monopoly of a common rival, the Great Eastern, the system resulted from the linking of a series of small, local lines of no particular significance. This strategy was devised to quell the suspicion of the rival until matters were so far advanced as to be too late. The resultant largely single-track line was initially known as the Eastern and Midland Railway until the setting up of a joint committee to administer the line and to complete some vital sections in 1893. This was known as the Midland and Great Northern Joint Railways Committee and the names of the sponsoring companies were then plain for all to see.
Interestingly enough, the differences with the Great Eastern were overcome in the years that followed to the extent that a new joint railway was formed in co-operation with the rival, opening up new areas of countryside at a less costly price. The new railway was known as the Norfolk and Suffolk Joint Railway and was unique in British railway history for one of the partners was itself a joint railway! At the same time, the Great Eastern won running powers over the M&GN as far as Sheringham, a move which, in itself, helped keep the old competitive spirit alive.
Following this agreement with the Great Eastern, the M&GN settled down to a lengthy period of untroubled service. Freight, ever important in an area rich in agricultural produce, fish and flowers and dependent on elsewhere for coal and manufactured goods, naturally travelled the M&GN route to the Midlands and North—except when the Great Eastern offered more competitive rates! For passengers, the line provided local services between the towns of North Norfolk and the northern part of the Fens and through express services for businessman and holidaymaker alike: not only to London but destinations as diverse as Leeds, Sheffield, Liverpool, Birmingham, Leicester, Derby, Nottingham and Manchester. Indeed, for several years the last three destinations were offered a choice of competing services over the differing routes of each of the two owners! In summary, the M&GN offered a cross-country link second to none.
The line continued in joint ownership following the 1923 Grouping, the new owners being the LMS and the LNER, and the event (apart from the gradual adoption of a dark brown livery for the locomotives) largely passed the M&GN by. It wasn’t until 1st October 1936 that things changed: following a review of joint operations, the LNER took over the administration of the line (although the LMS retained its say in general policy matters). The new masters steadily scrapped the locomotive stock, the largely Midland designs being non-standard, and tried all types of substitutes on the line. However, the most successful of the replacements—the LMS designed 4MT 2-6-os—had to wait until nationalisation in 1948 permitted Midland loco practice to creep back!
In later years, diesel multiple units took over the local workings, but rationalisation was in the air. The M&GN’s detractors pointed out that every place it benefited was equally served by the GE line and that two railways were an extravagance in an area ofsuch low population. With the motor vehicle becoming available to a mass market, perhaps the line had to go but closure of virtually all of it in 1959—Britain’s first main-line closure—came as  shock.