[11] The Northern line building was designed by Thomas Phillips Figgis,[12] and was rebuilt several times until the current structure opened in 2003.

Similar proposals have been revived on several occasions; in 2014 TfL ran a consultation on an extension to Hayes and Beckenham Junction, which is still under consideration.

[15][16] The BS&WR station building remains much as originally constructed and is a typical Leslie Green structure.

[11] The main alteration is a modern glass-sided and glass-topped flat-roofed extension abutting the original western elevation, giving access to three of the six arches.

These arches, in a classic deep-red faience style,[15] formed the original perimeter: two are infilled with street-facing shops.

[12][19] This Northern line ticket hall was rebuilt at the start of the 21st century, reopening on 12 December 2003 following 2 years of upgrade work.

[1][2] From inside the station, the northern exit is labelled "London South Bank University"[24] and emerges at the southern tip of the triangular campus.

[12] The original C&SLR tiles dating from 1890 remain on the tunnel roofs of the Northern line platforms, albeit now covered over by the new cable-management system.

[9] The typical off-peak service (as of January 2015) in trains per hour (tph) is 10tph northbound to each of High Barnet[29][30] and Edgware[29][30] and 20tph southbound to Morden.

[37] The entire route was approved on 25 July 1890[38][note 6] and the station opened on 18 December 1890 as part of the first successful deep-level tube railway.

[41][note 7] The new route and the first section of the northern extension from Borough to Moorgate opened on 25 February 1900, and the King William Street diversion was closed.

[49][note 10] In November 1891, a private bill was presented to Parliament for the construction of the Baker Street and Waterloo Railway (BS&WR).

[50] The railway was planned to run entirely underground from Marylebone[51] to Elephant & Castle[52] via Baker Street and Waterloo[50] and was approved in 1900.

[29] A collapse on the same day, caused when a train hit temporary shoring near Elephant & Castle, filled the tunnel with wet gravel.

"[62][63] The interchange between the Bakerloo and Northern lines has long been criticised by local residents for its lack of escalators, its winding passageways and its two separate station entrances.

[66] The upgrade and expansion work will include a new station entrance and ticket hall facing Elephant Square, three new escalators, and lifts providing step-free access to the Northern line platforms.

[67] The new entrance would also improve the interchange between the Underground and Elephant & Castle railway station, with a more direct route through the new development.

[76][note 12] In the 1950s there was a brief revival of the plan, in which it was proposed that Elephant & Castle would not be altered and the additional turn-round capacity would be provided by making Camberwell a three-platform terminus.