The BT Tower, one of London's most famous landmarks, was opened by the then Prime Minister Harold Wilson 40 years ago on 8 October 1965.
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Originally known as the Post Office Tower, it was the UK's highest building at the time, standing 189 metres tall including a 12 metre London Weather Centre radar mast.
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The tower was designed to meet the increased demands of broadcasting by allowing the use of microwaves instead of landlines for transmitting television signals.
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Today the tower handles around 3,000 switched calls per day, 99 per cent of all live football and terrestrial television passes through it and it is a Grade II listed building.
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It cost £2.5m to build and can stand up to 23 centimetres shorter in winter than it is in summer - because of contraction and expansion - and is designed to sway no more than 20 centimetres each way in winds up to 100mph.