 After the war , plans to complete the Northern Heights project were reviewed but no work was carried out . Maintenance works and reconstruction of war damage on the existing network had the greatest call on London Underground funds . Funds for new works were severely limited and priority was given to the completion of the western and eastern extensions of the Central line to West Ruislip , Epping and Hainault . Despite being shown as under construction on underground maps as late as 1950 , work never restarted on the unimplemented parts of the Northern Heights project . 
