Works were completed from Highgate to High Barnet and Mill Hill East and that section was incorporated into the Northern line.

Works on the tracks between Finsbury Park and Alexandra Palace were halted and the LNER continued to be operate the line.

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.

[5] Despite being shown as under construction on underground maps as late as 1950,[n 1] work never restarted on the unimplemented parts of the Northern Heights plan.

[10] British Railways (the successor to the LNER) closed the line temporarily from 29 October 1951 until 7 January 1952,[2] before the last passenger services ran between Finsbury Park and Alexandra Palace on 3 July 1954.