The M&StJWR was a separately promoted railway partly funded and operated by the Metropolitan Railway. The line north from the MR's station at Baker Street was approved in 1864 and was to continue to a station next to the London and North Western Railway's Finchley Road station. Financial difficulties meant the scope of the line was reduced to a single track line and only progressed as far as Swiss Cottage, which opened with the line on 13 April 1868. On 26 April 1868, two trains collided head-on at the station. This was the result of a signaller's error, which caused an arriving train to be misrouted to the platform where another train stood awaiting departure. Three people were injured. In 1873, the M&StJWR was authorised to extend its railway to Kingsbury and to add a second track between Swiss Cottage and Baker Street. The first extension to West Hampstead opened on 30 June 1879 as an interim single track shuttle service from Swiss Cottage before works to Willesden Green were completed and opened on 24 November 1879. The MR took control of the M&StJWR on 1 April 1882. The line was subsequently extended in stages to reach Watford, Aylesbury, Chesham and Uxbridge. In the 1920s, the MR demolished the street-level station building on the west side of Finchley Road, and replaced it with a shopping arcade and three entrances down to the station. The structure was built to the designs of C. W. Clark. By 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. To ease this congestion, a new section of deep-level tunnel was constructed between Finchley Road station and the Bakerloo line tunnels at Baker Street. The Metropolitan line's Stanmore branch services were then transferred to the Bakerloo line, with effect from 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. For the new deep-level route, a new Bakerloo line station named Swiss Cottage was opened adjacent to the existing Metropolitan line station. For a time, they operated as a single station. This arrangement was short-lived, however, and the Metropolitan line Swiss Cottage station was closed after the last train on 17 August 1940 as a wartime economy. On 1 May 1979, the Stanmore branch of the Bakerloo line was transferred to the new Jubilee line. The MR station building was demolished in the 1960s to allow the widening of Finchley Road, but the former platform area still exists in part.
Before the line was constructed, the M&StJWR received authorisation in 1865 to continue the line northwards from Finchley Road to a station at Hampstead. This appeared on some maps. The scheme was cancelled in 1870. A section of tunnel was built north of Swiss Cottage station for the Hampstead extension, most of which was used for the later extension to the north-west. A short length towards Hampstead was unused. This is still visible today when travelling on a southbound Metropolitan line service.
