Further information: In 1935 London Transport planned, as part of its “New Works Programme", to take over the line from LNER together with the LNER's routes from Finsbury Park to Edgeware and High Barnet, to modernise it for use with electric trains and amalgamate it with the Northern line.

Works to modernise the track began in the late 1930s and were advanced but were interrupted by the Second World War. Subsequent completion of works from Highgate to High Barnet and Mill Hill East ended with this section being incorporated into the Northern line between 1939 and 1941. Continued works on the section between Finsbury Park and Alexandra Palace were postponed and the line continued under the operation of the LNER. Due to wartime economies services were reduced to rush hours only, post war dwindling passenger numbers and a shortage of funds led to the cancellation of the unfinished works in 1950 and passenger services to Muswell Hill station were ended by British Railways on 3 July 1954 along with the rest of the line between Finsbury Park and Alexandra Palace.

The line was used for goods until complete closure on 18 May 1957. The track was removed and the platforms and station buildings were demolished. The line between Muswell Hill and Finsbury Park is now a linear park, the Parkland Walk.