Parliamentary approval for a line from Wimbledon to Sutton had been obtained by the Wimbledon and Sutton Railway (W&SR) in 1910 but work had been delayed by World War I. From the W&SR's inception, the Metropolitan District Railway (MDR) was a shareholder of the company and had rights to run trains over the line when built. In the 1920s, the London Electric Railway (LER, precursor of London Underground) planned, through its ownership of the MDR, to use part of the route for an extension of the City and South London Railway (C&SLR, now the Northern line) 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 LER giving up its rights over the W&SR route. The SR subsequently built the line, one of the last to be built in th