 On 1 January 1948 , almost all railways in Britain — including the London Transport Passenger Board and the London and North Eastern Railway — were nationalised under the Transport Act 1947 . The LPTB became the London Transport Executive ( LT ) , and the LNER became a part of British Railways . In the Greater London Plan of 1944 Sir Patrick Abercrombie had strongly recommended a halt to further modern development in Chesham and along the Chess Valley to preserve the sensitive local environment , and there was thus little prospect for growth in passenger numbers on the branch . 
