By the mid-1930s, the London Underground’s Metropolitan line was suffering from congestion caused by the limited capacity of its tracks between Baker Street and Finchley Road stations. To relieve this pressure, a tunnel was constructed between the Bakerloo line’s platforms at Baker Street and Finchley Road and three Metropolitan line stations (Lord’s, Marlborough Road and Swiss Cottage) were replaced with two new Bakerloo stations (St. John’s Wood and Swiss Cottage). The Bakerloo line took over the Metropolitan line’s service to Stanmore on 20 November 1939, as noted on the poster.
The poster itself is a striking piece of graphic design, with bold colours, rough brushed typography and an unusual black variant of the famous roundel with the circle and bar separated from each other. The style of Beck’s diagram (then only 6 years old) is referenced, but not copied faithfully. Interestingly, the typeface used seems to be closer to Gill Sans than Johnston.