Mill Hill East is a London Underground station in Mill Hill in the London Borough of Barnet, north London. The station is the terminus and only station of a single-track branch of the Northern line from Finchley Central station and is in Travelcard Zone 4. It is the least used station on the Northern line with million passengers in . The station was opened in 1867 as part of the Great Northern Railway's line between Finsbury Park and Edgware stations. As part of London Underground's partially completed Northern Heights plan, main line passenger services ended in 1939 and Northern line trains started serving the station in 1941. History Main line Mill Hill East station was built by the Edgware, Highgate and London Railway (EH&LR) on its line from Finsbury Park station to Edgware station. Before the line was opened it was purchased in July 1867 by the larger Great Northern Railway (GNR), whose main line from King's Cross ran through Finsbury Park on its way to Potters Bar and the north. The station, originally named Mill Hill, opened along with the railway to Edgware on 22 August 1867 in what was then rural Middlesex. The line was built as a double track formation, but only a single track was laid, with the intention of doubling the track when traffic developed. When the GNR opened a branch from Finchley Central to High Barnet in April 1872, traffic on that section was greater and the second track between Finchley Central and Edgware was never laid. For most of its history the service between those two stations was operated as a shuttle. After the 1921 Railways Act created the Big Four railway companies, the GNR became part of the London and North Eastern Railway (LNER) in 1923. The station was given its present name on 1 March 1928. Northern Heights project In 1935, the London Passenger Transport Board (LPTB) announced a proposal, which became known as the Northern Heights project, to take over the LNER lines from Finsbury Park to Edgware, High Barnet and Alexandra Palace, and link them to both the Northern line at East Finchley and to the Northern City Line at Finsbury Park. Reconstruction of the line from Finchley Central to Edgware with double tracks began in 1938. The line and Mill Hill East station were closed for electrification on 11 September 1939. Following the outbreak of the Second World