Northern line
After the UERL and the Metropolitan Railway (MR) were brought under public control in the form of the London Passenger Transport Board (LPTB) in 1933, the MR's subsidiary, the Great Northern & City Railway, which ran from Moorgate to Finsbury Park, became part of the Underground as the Northern City Line. In preparation for the Northern Heights Plan, it was operated as part of the Northern line, although it was never connected to it.