Reached its name via the North Metropolitan Railway (1853 incorporated). The company was incorporated again on the 7th August 1854. The GWR was the backer and was impatient at slow building progress. It wanted it to use broad gauge but agreed to mixed. The GWR worked the line from its opening on 30 September 1863. Worked both mainline and underground railway. Company expanded and reached Aylesbury. Electrics workings begain in 1905. On 1 July 1933 it became part of the London Passenger Transport Board.