Railway following the Railways Act 1921. In 1925 the Southern Railway decided to adopt a third rail electrification system and the lines through the station were converted between June 1928 and September 1929. When sectorisation was introduced in the 1980s, the national rail lines were served by Network SouthEast until the privatisation of the British Railways in the 1990s to the Connex South Central franchise, replaced by the current operator in 2000. The station has a high brick wall along Balham Station Road on which four cold cast bronze reliefs are mounted and titled "Impressions of Balham". These depict local residents and everyday scenes. They were conceived and constructed by Christine Thomas and Julia Barton and installed in 1991 for Wandsworth Borough Council. London Underground station The station opened on 6 December 1926 as part of the Morden extension of the City and South London Railway south from . The line and other stations on the extension had opened earlier, on 13 September 1926. The station is between and stations in the Northern line. Along with the other stations on the Morden extension, the building was designed by architect Charles Holden. They were Holden's first major project for the Underground. He was selected by Frank Pick, general manager of the Underground Electric Railways Company of London (UERL), to design the stations after he was dissatisfied with designs produced by the UERL's own architect, Stanley Heaps. The Underground station buildings are listed Grade II. The station has entrances on the east and west sides of Balham High Road linked by a pedestrian subway. The modernist designs of each building take the form of double-height screens clad in white Portland stone with three-part glazed screens in the centres of the façades divided by columns of which the capitals are three-dimensional versions of the Underground roundel. The central panel of the screens contain a large version of the roundel. Balham is the only station on the Morden branch of the Northern Line conjoined to a National Rail station. Second World War During the Second World War, Balham was one of many deep tube stations designated for use as a civilian air raid shelter. On the evening of 14 October 1940, a 1,400 kg semi-armour piercing fragmentation bomb fell on the road above the northern end of the platform tunnels, creating a large crater into which an out-of-service bus then crashed. The northbound platform