Editing Northern line (section)

===Extensions===
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 used plans dating back to 1901 for the [[Charing Cross, Euston and Hampstead Railway#Hampstead Heath controversy|Edgware and Hampstead Railway]] (E&HR)<ref name=gazette_2>{{London Gazette |issue=27380 |date=26 November 1901 |page=8200}}</ref> which the UERL's subsidiary, the [[London Electric Railway]], had taken over in 1912.{{sfn|Horne|2009|p=28}} It extended the CCE&HR line from its terminus at Golders Green to Edgware in two stages: to [[Hendon Central tube station|Hendon Central]] in 1923 and to [[Edgware tube station|Edgware]] in 1924.{{sfn|Rose|2016}}{{sfn|Horne|2009|p=29}} The line crossed open countryside and ran mostly on viaduct from Golders Green to Brent and then on the surface, apart from a short tunnel north of Hendon Central.{{sfn|Horne|2009|p=29}} Five new stations were built to pavilion-style designs by [[Stanley Heaps]], head of the Underground's Architects Office, stimulating the rapid northward expansion of suburban developments in the following years.{{sfn|Day|Reed|2010|p=91}}

====Morden Extension====
The engineering of the Morden extension of the C&SLR from Clapham Common to Morden was more demanding; it runs in tunnels to a point just north of [[Morden tube station|Morden station]] which was constructed in a cutting. The line then goes under the wide station forecourt and public road outside the station to the depot. The extension was initially [[Sutton Underground Line Proposal|planned]] to continue to [[Sutton, London|Sutton]]<ref name=gazette_3>{{London Gazette |issue=32770 |date=24 November 1922 |pages=8314–8315}}</ref> over part of the route for the unbuilt [[Wimbledon and Sutton Railway]] (in which the UERL held a stake) but agreements were made with [[Southern Railway (Great Britain)|Southern Railway]] to end the extension at Morden. Southern Railway built the surface line from Wimbledon to Sutton in the 1930s via South Merton and St. Helier.{{#tag:ref|The stations that the C&SLR were to serve on the W&SR, would not have included all those subsequently built by the Southern Railway. [[Morden tube station (District Railway)|South Morden]] (not built), [[Sutton Common railway station|Sutton Common]], [[Cheam tube station|Cheam]] (not built) and [[Sutton (Surrey) railway station|Sutton]], would have been served, but [[Morden South railway station|Morden South]], [[St Helier railway station|St Helier]] and [[West Sutton railway station|West Sutton]] were not part of the UERL's plan.|group="nb"}} The tube extension itself opened in 1926 with seven new stations all designed by [[Charles Holden]] in a modern style. Originally Stanley Heaps was to design the stations, but after seeing the designs [[Frank Pick]] (Assistant Joint Manager of the UERL) decided that Holden should take over the project.<ref>{{cite web |title=Underground Journeys: Moving Underground |url=http://www.architecture.com/LibraryDrawingsAndPhotographs/Exhibitionsandloans/VARIBAArchitecturePartnershipexhibitions/UndergroundJourneys/MovingUnderground/MovingUnderground.aspx |work=architecture.com |publisher=[[Royal Institute of British Architects]] |access-date=20 February 2011 |archive-url=https://web.archive.org/web/20110504024751/http://www.architecture.com/LibraryDrawingsAndPhotographs/Exhibitionsandloans/VARIBAArchitecturePartnershipexhibitions/UndergroundJourneys/MovingUnderground/MovingUnderground.aspx |archive-date=4 May 2011}}</ref>

With the exception of Morden and [[Clapham South tube station|Clapham South]], where more land was available, the new stations were built on confined corner sites at main road junctions in areas that had been already developed. Holden made good use of this limited space and designed striking buildings. The street-level structures are of white [[Portland stone]] with tall double-height ticket halls, with the 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, creating a welcoming feel.<ref>{{cite web |title=Underground Journeys: South Wimbledon |url=http://www.architecture.com/LibraryDrawingsAndPhotographs/Exhibitionsandloans/VARIBAArchitecturePartnershipexhibitions/UndergroundJourneys/MovingUnderground/SouthWimbledon.aspx |work=architecture.com |publisher=[[Royal Institute of British Architects]] |access-date=20 February 2011 |archive-url=https://web.archive.org/web/20110707161011/http://www.architecture.com/LibraryDrawingsAndPhotographs/Exhibitionsandloans/VARIBAArchitecturePartnershipexhibitions/UndergroundJourneys/MovingUnderground/SouthWimbledon.aspx |archive-date=7 July 2011}}</ref> 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 building]]s.