The first exchange was to be called BLAckfriars, to serve the densely telephoned district south and west of St Paul's Cathedral.
In 1922 the GPO Engineer-in-Chief Colonel Purves recommended its adoption for London, as the first cost would be lower than the panel system and the equipment was similar to exchanges already installed.
The first director exchange, Holburn, (made by ATM) was cut over in London on 12 November 1927, and the system was subsequently installed in other large British cities.
[5] ATM obtained several overseas contracts for SXS exchanges, such as in 1920 for Buenos Aires, operated by the United River Plate Telephone Company.
GEC also won overseas contracts for New Delhi (India), Jerusalem and Haifa (Palestine), and China, the Irish Free State and Siam.