In the mid-1930s the Metropolitan line was suffering congestion at the south end of its main route where trains from its many branches were struggling to share the limited capacity of its tracks between Finchley Road and Baker Street stations. To ease this congestion a new section of deep-level tunnel was constructed between Finchley Road and the Bakerloo line tunnels at Baker Street station. The Metropolitan line's Stanmore branch services were then transferred to the Bakerloo line on 20 November 1939 and diverted to run into Baker Street in the new tunnels, thus reducing the number of trains using the Metropolitan line's tracks.
With the new deep tunnel route, a new Swiss Cottage Bakerloo line station was opened adjacent to the existing Metropolitan line's station and, for a time, these operated as a single station (platforms 1 and 2 were Metropolitan line, platforms 3 and 4 were Bakerloo line). This arrangement was short-lived, however, and the Metropolitan Line station was closed on 17 August 1940 as a wartime economy. With the opening of the Jubilee line in 1979, the Stanmore branch of the Bakerloo line, including the replacement Swiss Cottage station, was transferred to be part of the new Jubilee line.