Parliamentary approval for a line from Wimbledon to Sutton had been obtained by the Wimbledon and Sutton Railway in 1910 but work had been delayed by World War I. From the W&SR's inception, the District Railway was a shareholder of the company and had rights to run trains over the line when built. In the 1920s, the Underground Electric Railways Company of London planned, through its ownership of the DR and the City and South London Railway, to use part of the W&SR's route for an extension of the C&SLR to Sutton. The SR objected and an agreement was reached that enabled the C&SLR to extend as far as Morden in exchange for the UERL giving up its rights over the W&SR route. The SR subsequently built the line, one of the last to be built in the London area. The station opened on 5 January 1930 when full services on the line were extended from South Merton. In the original 1910 proposals, which predated the plans for the C&SLR extension and the London County Council's plan for the development of the St Helier estate, a different Morden station was to be built closer to the original centre of Morden village on the south side of Central Road. In the 1920s W&SR and LER proposals, that station was renamed "South Morden". When the Wimbledon to Sutton line was built by the SR, the planned W&SR station was replaced by Morden South and St Helier stations. Formerly, a siding served an Express Dairies bottling plant adjacent to the station. Until 1978 milk trains delivered milk to the plant for bottling and distribution. Shunting was latterly undertaken by Hunslet Engine Company "Yardmaster" locomotive No.HE5308/60 named David. The bottling plant closed in 1992. Morden South would have been a station on the proposed Northern line extension to North Cheam.
Services
Throughout the day Thameslink provide a service of 2 trains per hour to St Albans City via Wimbledon and 2 trains per hour to Sutton. Services to Sutton then continue on to St Albans City via Mitcham Junction. Some late evening services to St Albans are extended to Bedford. On Sundays, daytime services are extended to Luton. On weekdays there are also peak time services operated bySouthern. In the morning peak Southern services operate anticlockwise around the loop to London Bridge via Sutton and Mitcham Junction; and in the evening peak services run clockwise to London Bridge via Wimbledon and Tooting.
