Sometimes in London, when you think you're just looking at a normal door, window or decorative feature, you're not. You're looking at a front for something else. An object that masks a hidden world beneath.
Such is the case with one historic building which just happens to be named the Queen Elizabeth II International Conference Centre. If you look at the front of this building in Broad Sanctuary in the City of Westminster, expecting to see something that related to Queen Elizabeth II, you won't - apart from the sign on the door that is.
But there's a clue that's very easy to miss that might help you. It's in the form of a structure that looks like a round stone well at the front of the building. It's not a well at all, it is in fact an air vent for something that lies beneath.
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For here, during the height of the Cold War was the command centre for a network of tunnels carrying cables, relaying vital messages across London. Here was the Government's so-called "Federal" telephone exchange.
The Exchange had first opened back in 1940 to serve key government departments and personnel during the second World War. In 1951 reports indicate it moved to the Broad Sanctuary site opposite Westminster Abbey, beneath where the conference centre now sits.
Beneath the ground between 1950 and 1952, a massive concrete blockhouse was built here three or four storeys deep. It was designed to survive what seemed like the likely occurrence of an atomic bomb attack.
It had a 10ft thick concrete roof and was connected to the deep level cable communications system that connected up various secret locations across London. It would have been able to accommodate many government staff working the exchanges which in those days had to be operated by hand.
Bizarrely in 1953, the site above it was used as the temporary location for a press communication centre for the Queen's coronation. It was even later let to National Car Parks Ltd for Parking. All this time beneath the ground lay the citadel equipped with its own power supply, air conditioning, water supply and generators running 24 hours a day.
The Federal exchanged moved on in 1958 or the 1960s, but the structure remained buried beneath the ground. The conference centre was opened on the site in 1986. Few people know that it once housed a vital part of the government's wartime communications network.
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