In the 1950s, during the Cold War, with worries about the possibility of a nuclear attack, three secure secret underground telephone exchanges were built.  One was in London, known as Kingsway, the second in Manchester called Guardian and the third in Birmingham known as Anchor.  This structure is one of the ventilation shafts for the exchange that occupied a series of tunnels beneath the city centre.  One access point was via a lift at the rear of Telephone House.  The exchange was apparently used until the 1980s but today the tunnels are used to carry cables across the city.

It appears that the original building has been modified or added to over the years.  It looks as if it was built in three stages.  The original 1930s building seems to have been made up of three elevations on Newhall Street, Lionel Street and a wing from Lionel Street across what is today the back of the building.  Then it seems a much later 6-storey extension was added on Fleet Street.  Finally a 3-storey block was added to the top of the Fleet Street extension.