The BT Tower is a communications tower located in Fitzrovia, London, owned by BT Group. It has been previously known as the GPO Tower, the Post Office Tower and the Telecom Tower. The main structure is 177 metres (581 ft) high, with a further section of aerial rigging bringing the total height to 191 metres (627 ft). Its Post Office code was YTOW.
Upon completion in 1964, it overtook the Millbank Tower to become the tallest building in both London and the United Kingdom, titles that it held until 1980, when it in turn was overtaken by the NatWest Tower.
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 the General Post Office 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.