||This article needs additional citations for verification. (September 2007)|
|Ridership||252.310 million (2011/12)  passenger journeys|
|Colour on map||Black|
|Depot(s)||Edgware, Golders Green,
|Rolling stock||1995 Tube Stock
6 cars per trainset
|Line length||58 km (36 mi)|
For most of its length it is a deep-level tube line.[nb 1] It carries about 252,310,000 passengers per year, making it the second busiest line on the Underground. It is unique in having two different routes through central London - the Charing Cross branch, serving the central part of zone 1, and the Bank branch, serving the eastern part of that zone. Despite its name, it does not serve the northernmost stations on the network, though it does serve the southernmost station (Morden) as well as 16 of the system's 29 stations south of the River Thames. There are 50 stations on the line, 36 of them below ground.
The line has a complicated history, and the current complex arrangement of two northern branches, two central branches and the southern branch reflects its genesis as three separate railway companies, combined in the 1920s and 1930s. An extension in the 1920s used a route originally planned by a fourth company. Abandoned plans from the 1920s, to extend the line further southwards, and then northwards in the 1930s, would have incorporated parts of the routes of two further companies. From the 1930s to the 1970s, the tracks of a seventh company were also managed as a branch of the Northern line.[nb 2] An extension from Kennington to Battersea is now planned, which will give the line a second southern branch to go with its two northern and central branches.
- See City and South London Railway and Charing Cross, Euston and Hampstead Railway for detailed histories of these companies
The core of the Northern line evolved from two railway companies: the City & South London Railway (C&SLR) and the Charing Cross, Euston & Hampstead Railway (CCE&HR).
The C&SLR, London's first deep-level tube railway, was built under the supervision of James Henry Greathead, who had been responsible, with Peter W. Barlow, for the Tower Subway. It was the first of the Underground's lines to be constructed by boring deep below the surface and the first to be operated by electric traction. The railway opened in November 1890 from Stockwell to a now-disused station at King William Street. This was inconveniently placed and unable to cope with the company's traffic so, in 1900, a new route to Moorgate via Bank was opened. By 1907 the C&SLR had been further extended at both ends to run from Clapham Common to Euston.
The CCE&HR (commonly known as the "Hampstead Tube") was opened in 1907 and ran from Charing Cross (known for many years as Strand) via Euston and Camden Town (where there was a junction) to Golders Green and Highgate (now known as Archway). It was extended south by one stop to Embankment in 1914 to form an interchange with the Bakerloo and District lines. In 1913, the Underground Electric Railways Company of London (UERL), owner of the CCE&HR, took over the C&SLR, although they remained separate companies.
During the early 1920s, a series of works was carried out to connect the C&SLR and CCE&HR tunnels to enable an integrated service to be operated. The first of these new tunnels, between the C&SLR's Euston station and the CCE&HR's station at Camden Town, had originally been planned in 1912, but had been delayed by World War I. The second connection linked the CCE&HR's Embankment and C&SLR's Kennington stations and provided a new intermediate station at Waterloo to connect to the main line station there and the Bakerloo line. The smaller-diameter tunnels of the C&SLR were expanded to match the standard diameter of the CCE&HR and the other deep tube lines.
In conjunction with the works to integrate the two lines, two major extensions were undertaken: northwards to Edgware in Middlesex (now in the London Borough of Barnet) and southwards to Morden in Surrey (then in the Merton and Morden Urban District, but now in the London Borough of Merton).
Edgware Extension 
The Edgware extension utilised plans dating back to 1901 for the Edgware and Hampstead Railway (E&HR) which the UERL had taken over in 1912. It extended the CCE&HR line from its terminus at Golders Green to Edgware in two stages: to Hendon Central in 1923 and to Edgware in 1924. The line crossed undeveloped open countryside and was on the surface, apart from a short tunnel north of Hendon Central. Five new stations were constructed to pavilion-style designs by Stanley Heaps, stimulating the rapid northward expansion of suburban developments in the following years.
Morden Extension 
The engineering of the Morden extension of the C&SLR from Clapham Common to Morden was more demanding, running in tunnels to a point just north of Morden station, which was constructed in a cutting. The line then runs under the wide station forecourt and public road outside the station, to the depot. The extension was initially planned to continue to Sutton over part of the route for the unbuilt Wimbledon and Sutton Railway, in which the UERL held a stake, but agreements were made with the Southern Railway to end the extension at Morden. Southern Railway later built the surface line from Wimbledon to Sutton, via South Merton and St. Helier. The tube extension opened in 1926, with seven new stations, all designed by Charles Holden in a modern style. Originally, Stanley Heaps, head of the Underground's Architects Office was to design the stations, but after seeing these designs Frank Pick, Assistant Joint Manager of the UERL, decided Holden should take over the project. With the exception of Morden and Clapham South, where more land was available, the new stations were built on confined corner sites at main road junctions in already developed areas. Holden made good use of this limited space and designed impressive buildings. The street-level structures are of white Portland stone with tall double-height ticket halls, with the famous London Underground roundel made up in coloured glass panels in large glazed screens. The stone columns framing the glass screens are surmounted by a capital formed as a three-dimensional version of the roundel. The large expanses of glass above the entrances ensure that the ticket halls are bright and, lit from within at night, welcoming. The first and last new stations on the extension, Clapham South and Morden, include a parade of shops and were designed with structures capable of being built above (like many of the earlier central London stations). Clapham South was extended upwards soon after its construction with a block of apartments; Morden was extended upwards in the 1960s with a block of offices. All the stations on the extension, except Morden itself, are Grade II listed buildings.
The resulting line became known as the Morden–Edgware line, although a number of alternative names were also mooted in the fashion of the contraction of Baker Street & Waterloo Railway to "Bakerloo", such as "Edgmor", "Mordenware", "Medgway" and "Edgmorden". It was eventually named the Northern line in August 1937, reflecting the planned addition of the Northern Heights lines.
Great Northern & City Railway 
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.
The Northern Heights plan 
- See Edgware, Highgate and London Railway for a detailed history of that company
In June 1935, the LPTB announced the New Works Programme, an ambitious plan to expand the Underground network which included the integration of a complex of existing London and North Eastern Railway (LNER) lines north of Highgate through the Northern Heights. These lines, built in the 1860s and 1870s by the Edgware, Highgate and London Railway (EH&LR) and its successors, ran from Finsbury Park to Edgware via Highgate, with branches to Alexandra Palace and High Barnet. The line taken over would be extended beyond Edgware to Brockley Hill, Elstree South and Bushey Heath with a new depot at Aldenham. The extension's route was that planned for the unbuilt Watford and Edgware Railway (W&ER), using rights obtained from the earlier purchase of the W&ER (which had long intended an extension of the EH&LR Edgware route towards Watford). This also provided the potential for further extension in the future; Bushey's town planners reserved space in Bushey village for a future station and Bushey Heath station's design was revised several times to ensure this option would remain available in the future.
The project involved electrification of the surface lines (operated by steam trains at the time), the doubling of the original single-line section between Finchley Central and the proposed junction with the Edgware branch of the Northern line, and the construction of three new linking sections of track: a connection between Northern City Line and Finsbury Park station on the surface; an extension from Archway to the LNER line near East Finchley via new deep-level platforms below Highgate station; and a short diversion from just before the LNER's Edgware station to the Underground's station of the same name.
Intended service levels 
The peak-hour service pattern was to be 21 trains an hour each way on the Barnet branch north of Camden Town, 14 of them via the Charing Cross branch and seven via the Bank branch. 14 would have continued on beyond Finchley Central, seven each on the High Barnet and Edgware branches. An additional seven trains an hour would have served the Barnet branch, but continued via Highgate High-Level and Finsbury Park to Moorgate, a slightly shorter route to the City. It does not seem to have been intended to run through trains to the ex-Northern City branch from Edgware via Finchley Central. Seven trains an hour would have served the Alexandra Palace branch, to/from Moorgate via Highgate High-Level. In addition to the 14 through trains described, the ex-Northern City branch would have had 14 four-car shuttle trains an hour.
Progress of works 
Work began in the late 1930s, and was in progress on all fronts by the outbreak of World War II. The tunnelling northwards from the original Highgate station (now Archway) had been completed, and the service to the rebuilt surface station at East Finchley started on 3 July 1939, but without the opening of the intermediate (new) Highgate Station, at the site of the LNER's station of the same name. Further progress was disrupted by the start of the war, though enough had been made to complete the electrification of the High Barnet branch onwards from East Finchley over which tube services started on 14 April 1940; the new (deep-level) Highgate station finally opened on 19 January 1941. The single track LNER line to Edgware was electrified as far as Mill Hill East, including the Dollis Brook Viaduct, opening as a tube service on 18 May 1941 to serve the barracks there, thus forming the Northern line as it is today. The new depot at Aldenham had already been built and was used to build Halifax bombers. Work on the other elements of the plan was suspended late in 1939.
Preparatory work including viaducts and a tunnel had been started but not completed on the Bushey extension pre-war. After the war, the area beyond Edgware was made part of the Metropolitan Green Belt, largely preventing the anticipated residential development in the area, and the potential demand for services from Bushey Heath thus vanished. Available funds were directed towards completing the eastern extension of the Central line instead, and the Northern Heights plan was dropped on 9 February 1954. Aldenham depot was converted into an overhaul facility for buses.
The implemented service from High Barnet branch gave good access both to the West End and the City. This appears to have undermined traffic on the Alexandra Palace branch, still run with steam haulage to Kings Cross via Finsbury Park, as Highgate (low-level) was but a short bus ride away and car traffic was much lighter than it would become later. Consequently, the line from Finsbury Park to Muswell Hill and Alexandra Palace via the surface platforms at Highgate was closed altogether to passenger traffic in 1954. This contrasts with the decision to electrify the Epping-Ongar branch of the Central line, another remnant of the New Works programme, run as a tube-train shuttle from 1957. A local pressure group, the Muswell Hill Metro Group, campaigns to reopen this route as a light-rail service. So far there is no sign of movement on this issue: the route, now the Parkland Walk, is highly valued by walkers and cyclists, and suggestions in the 1990s that it could, in part, become a road were met with fierce opposition. Another pressure group has proposed using the track bed further north, as part of the North and West London Light Railway. The connection between Drayton Park and the surface platforms at Finsbury Park was eventually opened in 1976, the Northern City Line becoming part of British Rail.
The rural railway heritage of the High Barnet branch beyond Highgate can be seen in the design of many of the stations.
Recent developments 
In 1975, the Northern City Line, known by that time as the Highbury branch, was transferred from London Underground to British Rail; it is now served by First Capital Connect.
In 2003, a train derailed at Camden Town. Although no one was hurt, points and signals were damaged, and the junctions there were not used while repairs were under way: trains coming from Edgware worked the Bank branch only, and trains from High Barnet and Mill Hill East worked the Charing Cross branch only. This situation was resolved when the junctions reopened, after much repair work and safety analysis and testing, on 7 March 2004. A joint report by the Underground and its maintenance contractor Tube Lines concluded that poor track geometry was the main cause, and that, because of this, extra friction arising out of striations (scratches) on a newly installed set of points had allowed the leading wheel of the last carriage to climb the rail and so derail. The track geometry at the derailment site is a very tight bend and tight tunnel bore, which precludes the normal solution for this sort of geometry of canting the track by raising the height of one rail relative to the other.
On 7 July 2005 a defective train on the Northern line (causing its subsequent suspension) saved a Northern line train from being blown up as part of a terrorist attack on the London Underground and bus systems. Three trains on the Circle and Piccadilly lines were blown up. The Northern line bomber instead boarded a bus, which he later blew up.
On 13 October 2005 the entire Northern line service was suspended due to maintenance problems with the emergency braking system on the trains. A series of rail replacement buses was used to connect outlying stations with other Underground lines. Full service was restored on 18 October.
In October 2006, off-peak service between Mill Hill East and Finchley Central was cut back to a shuttle, except for a few weekend through trains.
From June 2006, the service between East Finchley and Camden Town was suspended for two non-consecutive weekends every month, with service on the Edgware branch suspended for the other two weeks. This was part of Tube Lines's redevelopment of some Edgware and High Barnet Branch stations, including replacement of track, signals, as well as station maintenance. This included refurbishment of all High Barnet branch stations from West Finchley to Camden Town.
On 13 August 2010, a defective maintenance train caused disruption on the Charing Cross branch, after it travelled four miles in 13 minutes without a driver. The train was being towed to the depot after becoming faulty. At Archway tube station, the defective train became detached and ran driverless until coming to a stop at an incline near Warren Street tube station. This caused morning rush-hour services to be suspended on this branch. All passenger trains were diverted via the Bank branch, with several not stopping at stations until they were safely on the Bank branch.
Rolling stock 
As part of the New Works Programme, the Northern Line was provided with 1938 stock. Today, all Northern line trains consist of London Underground 1995 Stock in the Underground livery of red, white and blue. In common with the other deep-level lines, the trains are the smaller of the two sizes used on the system. 1995 stock has automated announcements and quick-close doors. If the proposed split of the line takes place (estimated for 2018), 19 new trains will be added to the existing fleet.
Although other London Underground lines operate fully underground, the Northern line is unusual in that it is a deep-level tube line that serves the outer suburbs of South London yet there is only one station above ground (Morden tube station) while the rest of this part of the line is deep below ground. The short section to Morden depot is also above ground. This is partly because its southern extension into the outer suburbs was not done by taking over an existing surface line as was generally the case with routes like the Central, Jubilee and Piccadilly lines. Apart from the core central underground tunnels, part of the section between Hendon and Colindale is also underground. As bicycles are not allowed in tunnel sections (even if no station is in that section) as they would hinder evacuation, they are limited to High Barnet – East Finchley, the Mill Hill East branch, Edgware – Colindale and Hendon – Golders Green. There are also time-based restrictions.
High Barnet branch 
|High Barnet branch|
|High Barnet||1 April 1872||First Northern line train was 14 April 1940map 1|
|Totteridge and Whetstone||1 April 1872||First Northern line train was 14 April 1940map 2|
|Woodside Park||1 April 1872||First Northern line train was 14 April 1940map 3|
|West Finchley||1 March 1933||First Northern line train was 14 April 1940map 4|
|Mill Hill East (shuttle trains to and from Finchley Central)||22 August 1867||Closed 11 September 1939, reopened 18 May 1941map 5|
|Finchley Central||22 August 1867||First Northern line train was 14 April 1940map 6|
|East Finchley||22 August 1867||First Northern line train was 3 July 1939map 7|
|Highgate||22 August 1867||First Northern line train was 19 January 1941map 8|
|Archway||22 June 1907||Originally named Highgatemap 9|
|Tufnell Park||22 June 1907||map 10|
|Kentish Town||1868||First underground station 22 June 1907map 11|
Edgware branch 
|Edgware||18 August 1924||map 12|
|Burnt Oak||27 October 1924||map 13|
|Colindale||18 August 1924||map 14|
|Hendon Central||19 November 1923||map 15|
|Brent Cross||19 November 1923||Opened as Brent, renamed 20 July 1976map 16|
|Golders Green||22 June 1907||Originally a terminusmap 17|
|Hampstead||22 June 1907||map 18|
|Belsize Park||22 June 1907||map 19|
|Chalk Farm||22 June 1907||map 20|
Camden Town 
|Camden Town||22 June 1907||map 21|
|The junctions connecting the two northern branches of the Northern line to the two central branches are just south of Camden Town station. The station has a pair of platforms on each of the two northern branches, and southbound trains can depart toward either Charing Cross or Bank from either of the two southbound platforms without crossing over.|
Charing Cross branch 
|also known as the West End branch|
|Station||Image||Opened||Additional information and transfers|
|Mornington Crescent||22 June 1907||map 22|
|Euston||12 May 1907||Change for Northern line service via Bank and Victoria linemap 23|
|Warren Street||22 June 1907||Change for Victoria linemap 24|
|Goodge Street||22 June 1907||Opened as Tottenham Court Road, renamed 3 September 1908map 25|
|Tottenham Court Road||30 July 1900||Change for Central linemap 26|
|Leicester Square||15 December 1906||Change for Piccadilly line map 27|
|Charing Cross||10 March 1906||Northern line platforms opened 22 June 1907, change for Bakerloo linemap 28|
|Embankment ( Embankment Pier)||30 May 1870||Northern line extension opened 13 September 1926, change for Bakerloo, Circle and District linesmap 29|
|Waterloo ( Waterloo Pier, Festival Pier)||8 August 1898||Northern line began 1926, change for Bakerloo, Jubilee and Waterloo & City linesmap 30|
|Southbound trains on this branch often terminate at Kennington, which has a terminal loop|
Bank branch 
|also known as the City branch|
|Euston||12 May 1907||Change for Northern line service via Charing Cross and Victoria linemap 23|
|King's Cross St. Pancras ( Trains Gatwick and Luton)||1863||Northern line May 1907, change for Circle, Hammersmith & City, Metropolitan, Piccadilly and Victoria linesmap 31|
|Old Street||November 1901||Northern line platforms February 1904map 33|
|Bank||25 February 1900||Linked with Monument by escalator 18 September 1933, change for Central and Waterloo & City lines.map 35|
|London Bridge ( Trains to Gatwick and Luton) ( London Bridge City Pier)||25 February 1900||Original station opened 14 December 1836, change for Jubilee linemap 36|
|Borough||18 December 1890||map 37|
|Elephant and Castle||18 December 1890||Change for Bakerloo linemap 38|
Morden branch 
|Kennington||18 December 1890||map 39|
|Oval||18 December 1890||map 40|
|Stockwell||4 November 1890||Change for Victoria linemap 41|
|Clapham North||June 1900||map 42|
|Clapham Common||June 1900||Original terminus until 1926map 43|
|Clapham South||13 September 1926||map 44|
|Balham||6 December 1926||map 45|
|Tooting Bec||13 September 1926||Opened as Trinity Road, renamed 1 October 1950map 46|
|Tooting Broadway||13 September 1926||map 47|
|Colliers Wood||13 September 1926||map 48|
|South Wimbledon||13 September 1926||map 49|
|Morden||13 September 1926||Terminusmap 50|
The Northern line is serviced by four depots. The main one is at Golders Greenmap 51, adjacent to Golders Green tube station, while the second, at Morden,map 52 is south of Morden tube station and is the larger of the two. The other two are at Edgware and Highgate. The Highgate depot is on the former LNER branch to Alexandra Palace. There was originally a depot at Stockwell but it closed in 1915. There are sidings at High Barnet for stabling trains overnight.
Closed stations 
- King William Street (closed 1900, replaced by Bank)
- City Road (closed 1922)
- South Kentish Town (closed 1924)
- North End (also known as Bull & Bush - never opened – work stopped 1906)
Resited stations 
- Stockwell – new platforms resited immediately to the south of its predecessor with the 1922–1924 upgrade of the line.
- Euston – Northbound City branch platform resited on new alignment, with previous island platform converted to a single platform
- Angel – old island platform converted into a single platform, and a new alignment opened in 1992, along with a new entrance.
- London Bridge – the northbound tunnel and platform converted into a concourse, and a new northbound tunnel and platform built in the late 1990s to increase the platform and circulation areas in preparation for the opening of the Jubilee line.
Abandoned plans 
Northern Heights stations not transferred from LNER
- Highgate – High-level only
- Stroud Green
- Crouch End
- Cranley Gardens
- Muswell Hill
- Alexandra Palace
- Mill Hill (The Hale)
Bushey Extension stations not constructed
The Northern line was scheduled to switch to automatic train operation in 2012, using the same SelTrac system as used since 2009 on the Jubilee line and for a number of years on the Docklands Light Railway. Originally the work was to follow on from the Jubilee line so as to benefit from the experience of installing it there, but that project was not completed until spring 2011. Work on the Northern line was contracted to be completed before the 2012 Olympics. It is now being undertaken in-house, and TfL predicts the upgrade will be complete by the end of 2014. The first section of the line (West Finchley to High Barnet) was transferred to the new signalling system on 26 February 2013.
TfL has long aspired to split the Northern line into two separate routes.  Running trains between all combinations of branches and the two central sections, as at present, means only 20–22 trains an hour can run through each of the central sections, because merging trains have to wait for each other at the junctions. Completely segregating the routes will allow 32 trains an hour on all parts of the system. However, Camden Town tube station has to be rebuilt before this can be implemented, as the current station could not cope with the number of passengers changing trains. London Underground has failed to secure planning permission for this rebuild. Plans for a revised scheme for Camden Town station have been delayed by budget cuts.
Because the full split is not possible without a rebuilt Camden Town station, and the need to increase capacity remains, the current proposal is for a partial split by terminating all Charing Cross branch trains at Kennington during normal service. This would eliminate the need to co-ordinate train paths southbound when they merge at Kennington, and would enable the Morden-Bank branch to operate at the maximum capacity allowed by the new signalling system. This will not happen until the line has been resignalled, as only then will the full benefits of this plan be realised.
The owners of Battersea Power Station propose to redevelop it, with an extension of the line from Kennington to Battersea to serve the site. This has been approved by Wandsworth Council, and the extension could be open by 2020. On 11 November 2010 Wandsworth Council approved a detailed route for the extension, with an intermediate Nine Elms station at the junction of Wandsworth Road and Pascal Street. This was ratified by the Mayor of London on 22 December 2010.
In the long term, a full operational split of the line into two non-overlapping routes could lead to one or both being renamed and given a different colour on the Tube map.
See also 
- Leslie Green, architect of the Charing Cross, Euston and Hampstead Railway's early stations
- London deep-level shelters, most of which are under Northern line stations
- N5 night bus
- N20 night bus
- A "tube" railway is an underground railway constructed in a cylindrical tunnel by the use of a tunnelling shield, usually deep below ground level.
- The seven companies were 1. the City & South London Railway, 2. the Charing Cross, Euston & Hampstead Railway, 3. the Edgware, Highgate & London Railway, 4. the Edgware & Hampstead Railway, 5. the Watford & Edgware Railway, 6. The Wimbledon & Sutton Railway and 7. the Great Northern & City Railway.
- "LU Performance Data Almanac". Transport for London. 2011/12. Retrieved 1 August 2012.
- "Northern line facts". Transport for London. No date. Retrieved 12 March 2012.
- The London Gazette: . 22 November 1912. Retrieved 21 July 2008.
- The London Gazette: . 26 November 1901. Retrieved 21 July 2008.
- The London Gazette: . 24 November 1922. Retrieved 21 July 2008.
- "Underground Journeys: Moving Underground". www.architecture.com. Royal Institute of British Architects. Retrieved 20 February 2011.
- "Underground Journeys: South Wimbledon". www.architecture.com. Royal Institute of British Architects. Retrieved 20 February 2011.
- Wolmar 2004, "Reaching Out", p. 225.
- "London Tubes' New Names – Northern And Central Lines". The Times (47772): 12. 25 August 1937. Retrieved 18 May 2009.(subscription required)
- "Call for action on Northern Line". BBC News. 12 October 2005. Retrieved 10 June 2008.
- Stebbings, Peter (11 September 2006). "Five more years of Northern line pain". This Is Local London. Retrieved 26 August 2008.
- "Travel Delays as Tube Line Shut". BBC News (London). 13 October 2005. Retrieved 30 June 2008.
- "No Service on the Northern Line" (Press release). Transport for London. 13 October 2005. Retrieved 30 June 2008.
- "Map of Upgrades". Tube Lines. Archived from the original on 6 April 2008. Retrieved 30 June 2008.
- "Runaway train on London Tube's Northern Line". BBC News. 13 August 2010. Retrieved 18 August 2010.
- Runaway of an engineering train from Highgate 13 August 2010 (Technical report 09-2011). RAIB. 2011.
- Abbot 2010, pp. 57–58.
- "Bicycle Tube Map". Transport for London. January 2008. Retrieved 30 June 2008.[dead link]
- "Network Tests for New Signalling Systems" (Press release). Tube Lines. 24 August 2005. Archived from the original on 5 January 2008.
- "Operational and Financial Performance Report and Investment Programme Report – Third Quarter, 2012/13". Transport for London. 6 February 2013.
- "Northern line upgrade one step closer" (Press release). Transport for London. 26 February 2013.
- "Transport 2025 – Transport Vision for a Growing World". Transport for London. 11 November 2006. Retrieved 21 July 2008.
- Lydall, Ross (12 May 2010). "Northern line service divided in £312m bid to end overcrowding". London Evening Standard. Retrieved 21 March 2013.
- "Camden Town Redevelopment". Alwaystouchout.com. 25 January 2006. Retrieved 30 June 2008.
- "Battersea Power Station scheme approved" (Press release). London Borough of Wandsworth. 11 November 2010. Retrieved 12 November 2010.
- "Northern line extension". Transport for London. 8 May 2013. Retrieved 8 May 2013.
- "Mayor approves £5.5bn Battersea Power Station revamp". BBC News. 22 December 2010. Retrieved 6 April 2011.
- Abbott, James (February 2010). "Northern Line split planned". Modern Railways (Hersham: Ian Allan) 67 (737). ISSN 0026-8356.
- Blake, Jim; James, Jonathan (1993). Northern Wastes: Scandal of the Uncompleted Northern Line. London: North London Transport Society. ISBN 0-946383-04-9.
- Demuth, Tim (2004). The Spread of London's Underground (2 ed.). London: Capital Transport Publishing. ISBN 1-85414-277-1.
- Horne, Mike (1987). Northern Line: A Short History. London: Douglas Rose. ISBN 1-870354-00-1.
- Horne, Mike; Bayman, Bob (2009). The Northern Line: An Illustrated History (3 ed.). London: Capital Transport Publishing. ISBN 1-85414-326-3.
- Lee, Charles Edward (1973). Northern Line. London: London Transport. ISBN 0-85329-044-X.
- Lee, Charles Edward (1967). Sixty Years of the Northern. London: London Transport. OCLC 505166556.
- Lee, Charles Edward (1957). Fifty Years of the Hampstead Tube. London: London Transport. OCLC 23376254.
- Murphy, Simon (2005). Northern Line Extensions: Golders Green to Edgware, 1922–24. London: The History Press. ISBN 0-7524-3498-5.
- Wolmar, Christian (2004). The Subterranean Railway: How the London Underground Was Built and How It Changed the City Forever. London: Atlantic Books. ISBN 1-84354-023-1.
|Wikimedia Commons has media related to: Northern Line|
- "Northern Line". Clive's Underground Line Guides. 7 February 2008. Retrieved 11 July 2008.
- Muswell Hill Metro Group
- Northern line Route for the freeware train simulator BVE Trainsim
- "Northern Heights". Underground History. 23 February 2005. Retrieved 11 July 2008.
- Above-ground route of line from Morden to Edgware, constructed from Google StreetView
- Architectural history of London Underground during 1920-30s from the Royal Institute of British Architects
|West:||Crossings of the River Thames||East:|
|Hungerford Bridges||Charing Cross branch,
|Bakerloo Line, between Embankment and Waterloo|
|London Bridge||City branch,
and London Bridge