The GPO's (General Post Office) International Telephone Exchange.
Faraday ICCs Faraday 2A
Faraday ICC Summary Pages...
London, England, August 1961
Faraday 2A Tour...
London, England, circa 1981

Twenty years apart; it is thought that the two photos are the same switchroom, Faraday 2A.
In the 1960s, 2A was the only 'international' switchroom, the other switchrooms are listed as 'continental'.

Colour photo M.Knight.  Black & white photo 'Courtesy of Cable & Wireless Archive, Porthcurno'.