Bt Communication Tower

Radio tower, proposed in 1954 and built between 1961 and 1965 to designs by the Ministry of Public Buildings and Works Architect's Department. Eric Bedford was Chief Architect, with G R Yeats as senior architect in charge. S G Silhan served as senior structural engineer and J J Taylor as senior services engineer, both from MPBW, with Kenneth Holloway as Post Office engineer.

The building is a sleek reinforced concrete cylinder, 582 feet high with a 40-foot mast on top. The lower 130 feet are finished with board marks. It sits on deep raft foundations. At its core runs a reinforced concrete shaft resembling a chimney. The upper section of this central core is 22 feet in diameter with one-foot-thick walls, tapering outwards to an external diameter of 35 feet at the base where walls are 2 feet thick.

The lower seventeen floors contain equipment rooms, ventilation plant and offices. These are clad in a triple curtain wall system comprising stainless steel externally, glazed with Antisun glass. At the top, 103 feet of hospitality space occupies six levels, originally comprising observation floors, a restaurant, kitchen, and three further storeys housing plant rooms above. Aerials and dishes are mounted on circular galleries between 365 and 475 feet, positioned to allow maximum flexibility for adjustment and future equipment installation. The circular form has been maintained throughout the tower for consistency and to minimise wind resistance. The building's taper means the lower five floors are substantially smaller.

The ground floor entrance on Maple Street opens into a tower foyer with exhibition space on a concave link floor above. Lift lobbies lead to a 65-foot-diameter restaurant floor which originally revolved once every 25 minutes. Above this were a former cocktail lounge and weather station. The building originally allowed public access to galleries and restaurant but now serves only BT's guests. Interiors have been entirely refurbished. Telecommunications and servicing equipment are not included in the listing.

The tower was built as a centre for national and international telephone communication using ultra-high-frequency microwave transmission. The site was chosen behind the Museum Telephone Exchange, which was already the focal point of the telecommunications system and vision cables network for London, with cable connections to Broadcasting House. However, as telephone use soared in the 1950s and was correctly predicted to accelerate further, providing adequate cable links in central London became increasingly difficult. Radio telephones using low frequencies had long existed, but the use of high frequencies remained in its infancy. This tower's commitment to high-frequency transmission on a potentially massive scale placed it at the forefront of international design, representing "a considerable advance on any existing international centre" according to the Institution of Civil Engineers in 1965.

The sensitive equipment required exceptional structural stability to maintain accuracy in narrow beam transmission. Testing in the National Physical Laboratory wind tunnel proved the design would deflect only eleven inches in a hundred-mile-an-hour gale. The cylindrical shape further reduced wind resistance.

Height was raised to over 580 feet during construction to ensure the tower would be taller than London's newly erected office buildings. Its waves were relayed across Britain via a series of masts, the nearest being at Harrow. The design was carefully considered for elegance, with the Architects' Journal in 1966 noting that "the massing is a very welcome addition to the urban landscape."

The decision to include restaurant facilities was made only in mid-1961, reflecting a movement across North America and central Europe favouring landmark restaurants associated with radio masts. The comparable towers at Dortmund, Stuttgart and Vienna, though slightly earlier, served only as television transmitters. The Space Needle at the Seattle World's Fair, opened in 1962, was principally a place of entertainment. The restaurant and observatory floors provided structural stability and enhanced the Post Office's public image. Public access to observation floors ceased in 1971 and to the restaurant in 1980.

An office building along Cleveland Street and Maple Street forms a visual plinth to the tower with a supporting link on the fourth floor. It has its own entrance on the corner of Cleveland Street and is not included in the listing as it is not of special interest.

The tower was originally known as the Museum Radio Tower, subsequently as the Post Office Tower and Telecom Tower.