The Post Office Tower, now known as the BT Tower, is located in London's West End and was built as a communication facility to transmit radio and microwave signals. Construction began in 1961 and it opened five years later after an expenditure of £2.5 million. At 188 metres high it was the tallest building in Britain and retained this title until being overtaken by the Nat West Tower in 1981. It also contained a public viewing platform and just above it, on the 36th floor, was a revolving restaurant which from the start was leased and managed by Butlins and known as the 'topofthetower'. In fact Billy Butlin, along with Tony Benn, performed the official opening ceremony on May 16th 1966. In 1971 a terrorist bomb exploded which caused the viewing platform to be closed to the public, although the restaurant remained in operation and still under the control of Butlins until their lease expired in 1980.