The GPO 300-series was first introduced in 1937. Although later, after 1945, it became the GPO standard telephone, it was first conceived as an office telephone. It was in production until 1957 and there are many different versions.
Based on the famous Ericsson DBH1001 this was GPO’s first autonomous compact telephone, meaning it did not require a separate bell unit. It was made in several versions, with various button lay outs and was made in a handful of colours, specifically red, green, white and of course black.
An often told anecdote tells that the then prince of Wales, later briefly king Edward VII, visited an exhibit where he became rather impressed with the Ericsson DBH1001. He bought one and took it home to England.
Later GPO used this very design as the basis for the GPO300. It is however unclear whether the acquisition of the British heir to the throne influenced the decisions of the GPO in this matter. In any case the family resemblance is clear
GPO changed the handset to their standard model, the type 164. They did retain the subframe of the DBH1001, although the lay out was not exactly the same.