LONDON - OCTOBER 17: A worker passes a redundant telephone exchange that used to carry the transatlantic hotline between the United States and the Soviet Union in a formely secret air raid tunnel on October 17, 2008 in London. The once secret tunnels were built 100 feet under central London in 1940 as fully equipped air raid shelters and could accommodate 8000 people. They have since been used by MI6 and the Public Records Office to hold 400 tons of secret documents. Current owners British Telecom (BT) are now seeking a buyer as the tunnels are surplus to requirements.