BT Tower

20th century

The tower was commissioned by the General Post Office (GPO). Its primary purpose was to support the microwave aerials then used to carry telecommunications traffic from London to the rest of the country, as part of Britain's microwave network.

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 25 centimetres (10 in) in wind speeds of up to 150 km/h (95 mph). Initially the first 16 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, and owing to the building's height and its having a tower crane jib across the top virtually throughout the whole construction period, it gradually became a very prominent landmark that could be seen from almost anywhere in London. In August 1963 there was even a question raised in parliament about the crane. Doctor Reginald Bennett MP asked the Minister of Public Building and Works how, when the crane on the top of the new Post Office tower had fulfilled its purpose, he proposed to remove it. Mr Geoffrey Rippon replied, "This is a matter for the contractors. The problem does not have to be solved for about a year but there appears to be no danger of the crane having to be left in situ."

The tower was topped out on 15 July 1964 and officially opened by the then Prime Minister Harold Wilson on 8 October 1965. The main contractor was Peter Lind & Co Ltd.

The tower was originally designed to be just 111 metres (364 ft), 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 on the 34th floor, called the Top of the Tower and 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. Tony Benn also designated the tower a mascot of UCL after lobbying by students. Comedian Pat Condell washed dishes in the kitchen for his first job.

A bomb, responsibility for which was at first blamed on the Provisional IRA, exploded in the roof of the men's toilets at the Top of the Tower restaurant on 31 October 1971. In fact, the bomb had been placed there by members of the Angry Brigade, an anarchist collective. The restaurant was closed to the public for security reasons in 1980, the year in which Butlins' lease eventually expired. Public access to the building ceased in 1981. The tower is sometimes used for corporate events such as a children's Christmas party in December, Children in Need, and other special events; even though it is closed the tower retains its revolving floor, providing a full panorama over London and the surrounding area.

Secrecy

Due to its importance to the national communications network, the location of the tower was designated an official secret. In 1978 the journalist Duncan Campbell was tried for collecting information about secret locations, and during the trial the judge ordered that the sites could not be identified by name; the Post Office Tower could only be referred to as 'Location 23'. In February 1993 the MP Kate Hoey drew attention to the supposed secrecy and claimed parliamentary privilege to reveal its location.

It is often said that the tower did not appear on Ordnance Survey maps, despite being a 177-metre (581 ft) tall structure in the middle of central London that was open to the public for about 15 years. However, this is incorrect; the 1:25,000 (published 1971) and 1:10,000 (published 1981) Ordnance Survey maps show the tower. It is also shown in the London A-Z street atlas for 1984.

21st century

The tower is still in use, and is the site of a major UK communications hub. Microwave links have been replaced by subterranean optical fibre links for most mainstream purposes, but the former are 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 above the former revolving restaurant, with the kitchens on floor 35.

A renovation in the early 2000s introduced a 360° coloured lighting display at the top of the tower. Seven colours were programmed to vary constantly at night and intended to appear as a rotating globe to reflect BT's "connected world" corporate styling. The coloured lights give the tower a distinctive appearance on the London skyline at night. In October 2009, a 360° full-colour LED-based display system was installed at the top of the tower, to replace the previous colour projection system. The new display, referred to by BT as the "Information Band", is wrapped around the 36th and 37th floors of the tower, 167 m (548 ft) up, and comprises 529,750 LEDs arranged in 177 vertical strips, spaced around the tower. The display is the largest of its type in the world, occupying an area of 280 m² (3,000 sq ft) and with a circumference of 59 m (194 ft). The display is switched off at 10.30pm each day. On 31 October 2009 the screen began displaying a countdown of the number of days until the start of the London Olympics in 2012.

In October 2009, The Times reported that the rotating restaurant would be reopened in time for the 2012 London Olympics. However, in December 2010, it was further announced that the plans to reopen had now been 'quietly dropped' with no explanation as to the decision. For the tower's 50th anniversary, the 34th floor was opened for three days from 3 to 5 October 2015 to 2,400 winners of a lottery.

The BT Tower was given Grade II listed building status in 2003. Several of the defunct antennas attached to the building could not be removed unless the appropriate listed building consent was granted, as they were protected by this listing. In 2011 permission for the removal of the defunct antennas was approved on safety grounds as they were in a bad state of repair and the fixings were no longer secure. In December 2011 the last of the antennas was removed leaving the core of the tower visible.

Entry to the building is by two high-speed lifts which travel at 7 metres per second (16 mph), reaching the top of the building in under 30 seconds. An Act of Parliament was passed to vary fire regulations, allowing the building to be evacuated by using the lifts – unlike other buildings of the time.

The tower is being used in a study to help monitor air quality in the capital. The aim is to measure pollutant levels above ground level to determine their source. One area of investigation is the long-range transport of fine particles from outside the city.

Appearances in fiction