 The route to Aylesbury and the Chesham branch survived Pick 's cutbacks to the Metropolitan line , but the former Metropolitan Railway 's routes in Buckinghamshire , and in particular the Chesham line , were increasingly regarded as an expensive anomaly by London Transport . After 1937 the operation of all steam services north of Rickmansworth was passed to the London & North Eastern Railway ( LNER ) . The LNER retained Metropolitan Railway E Class locomotives to work the Chesham branch , but other steam services on the former MR were operated by LNER N5 Class locomotives . 
