The BT Tower is a tall cylindrical building in London, England. The tower is located at 60 Cleveland Street, Fitzrovia. It has been previously known as the Post Office Tower and the British Telecom Tower. The main structure is tall, with a further section of aerial bringing the total height to . Contrary to popular belief, it is not the same as the BT Centre (the national headquarters of BT).
It replaced a much shorter steel lattice tower which had been built on the roof of the neighbouring Museum telephone exchange in the late 1940s to provide a television link between London and Birmingham. The taller structure was required to protect the radio links' "line of sight" against some of the tall buildings in London then in the planning stage. These links were routed via other GPO microwave stations at Harrow Weald, Bagshot, Kelvedon Hatch and Fairseat, and to places like the London Air Traffic Control Centre at West Drayton.
The tower was designed by the architects of the Ministry of Public Building and Works: the chief architects were Eric Bedford and G. R. Yeats. Typical for its time, the building is concrete clad in glass. The narrow cylindrical shape was chosen because of the requirements of the communications aerials: the building will shift no more than in wind speeds of up to 150 km/h (95 mph). Initially the first sixteen floors were for technical equipment and power, above that was a 35 metre section for the microwave aerials, and above that were six floors of suites, kitchens, technical equipment and finally a cantilevered steel lattice tower. To prevent heat build-up the glass cladding was of a special tint. The construction cost was £2.5 million.
Construction began in June 1961. The tower was topped out on 15 July 1964 and officially opened by Prime Minister Harold Wilson on 8 October 1965. The building contractors were Peter Lind & Company.
The tower was originally designed to be just , and its foundations are sunk down through 53 metres of London clay and are formed of a concrete raft 27 metres square, a metre thick, reinforced with six layers of cables on top of which sits a reinforced concrete pyramid.
The tower was officially opened to the public on 16 May 1966 by Tony Benn and Billy Butlin. As well as the communications equipment and office space there were viewing galleries, a souvenir shop, and a rotating restaurant, the "Top of the Tower", on the 34th floor, operated by Butlins. It made one revolution every 22 minutes. An annual race up the stairs of the tower was established and the first race was won by UCL student Alan Green.
A bomb, responsibility for which was claimed by the Provisional IRA, exploded in the roof of the men's toilets at the Top of the Tower restaurant on 31 October 1971. The restaurant was closed to the public for security reasons in 1980, the year in which the Butlins' lease eventually expired. Public access to the building ceased in 1981. The Tower is sometimes used for BT Corporate events, but is not available for hire or use by outside companies. The closure of the Tower restaurant to the public means London has no revolving restaurant of the type common in major cities throughout the world.
The tower is still in use, and is the site of a major UK communications hub.
Microwave links have been replaced by Subterranean fibre optic links for most mainstream purposes, but the former is still in use at the tower. The second floor of the base of the tower contains the TV Network Switching Centre which carries broadcasting traffic and relays signals between television broadcasters (including the BBC), production companies, advertisers, international satellite services and uplink companies.
The outside broadcast control is located about the former revolving restaurant, with the kitchens on floor 35.
A renovation in the 2000s installed coloured lighting projecting onto a new 360-degree light panel, extending out from the old light boxes, bearing the company logo, as part of BT's "connected world" corporate styling. Seven colours are programmed to vary constantly at night and are intended to appear as a rotating globe. The success of this is debatable but the building's night appearance is now more distinctive. The tower has always been a useful late-night navigational beacon for nearby residents, especially the numerous university halls within walking distance.
Until the mid-1990s, the building was officially a secret, and did not appear on official maps. Its existence was finally "confirmed" by Kate Hoey, MP, on 19 February 1993: "Hon. Members have given examples of seemingly trivial information that remains officially secret. An example that has not been mentioned, but which is so trivial that it is worth mentioning, is the absence of the British Telecom tower from Ordnance Survey maps. I hope that I am covered by parliamentary privilege when I reveal that the British Telecom tower does exist and that its address is 60 Cleveland Street, London.
The BT Tower was given Grade II listed building status in 2003, several of the now defunct antennas located on the building now cannot be removed, as they are protected by this listing.
Entry to the building is provided by two high-speed lifts which travel at 6 metres per second, reaching the top of the building in 30 seconds. Interestingly, an Act of Parliament was passed to vary fire regulations, allowing the building to be evacuated by using the lifts — it is the only building in the country where this is permitted.
BT Tower in London is being used in a major study to help improve the air quality in the capital - with the aim of reducing serious effects on human health.