BT Tower, now a Grade II listed building (formerly known as the Post Office Tower) was originally opened to staff by Prime Minister Harold Wilson MP and the then Postmaster-General, Anthony Wedgwood Benn on Friday 8 October 1965.
Widely acclaimed, the Tower was Britain’s highest building, standing at 620 ft (189 metres), including a 40 ft (12 metre) lattice aerial on top of it, until the construction of the Nat West Tower which was completed in 1980. BT Tower is now the seventh tallest structure in London, the tallest being One Canada Square at Canary Wharf (completed in 1991) at 237 metres.
The Tower was initially designed to carry aerials for the Post Office microwave network. It was built so tall because the microwave signals need an unobstructed route between each station, clear of the highest buildings and surrounding hills. One of its key functions was to help meet the growing demands of broadcasting, enabling the use of microwaves instead of traditional landlines for transmitting television signals. It also attracted much attention and admiration for its ‘Top of the Tower’ revolving restaurant sited on the 34th floor. Revolutionary at the time, some 105,000 dined there during the first year of opening. Still in full working order today, the 3-metre wide revolving segment spins through 360º every 22 minutes, a speed of 0.17 km/h.
Forty years on, the Tower remains an important part of the BT network and handles around one million switched calls, around 3,000 a day. 99% of all live football and most terrestrial television passes through the BT Tower.
David Hay, Head of BT Heritage, comments: “The tower is an iconic symbol of London, that everybody immediately recognises and, though taller buildings now exist, it is viewed with great affection by the general public. Whilst declared a national monument in 2001 by English Heritage, and listed by the Government in 2003 as ‘a cultural and architectural icon of Harold Wilson's 'white heat of technology', it still plays as important a role in the UK’s communications as it did in 1965.”
Construction of the tower began in 1961, costing £2.5 million – a small sum by today’ standards. It weighs 13,000 tons, including 95 tons of high tensile steel in the base and 695 tons of mild steel in the structure, and contains 50,000 square feet of glass. It was designed to sway no more than 20 centimetres (almost 8 inches) each way in winds up to 100 mph. Heat and cold cause the structure to expand and contract. The BT Tower can be as much as 23 centimetres shorter in the winter than it is in the summer.
Originally open to the public, during its first year the Tower was visited by almost one million visitors and quickly became one of London’s most popular tourist attractions. Visitors were transported by the tower's two lifts, which are still among the fastest in Europe, travelling at 6 metres per second. During that first year alone the lifts travelled almost 70,000 kilometres. The BT Tower remains the only building in the country which is allowed to be evacuated by lift (an oddity which required Parliamentary legislation to be passed).
The Tower has had its fair share of dramatic events, not least of all on 31 October 1971 when a bomb exploded on the 31st floor. The result of the bombing was a tightening of security that left the Tower largely closed to the public on a permanent basis. However, the restaurant remained in operation until 1980, when that too was closed to the public for security reasons, except for hospitality events and charity fund-raising functions, such as Comic Relief and BBC television’s Children In Need fund-raiser that takes place every November.