BT Tower

The General Post Office commissioned the tower to carry the microwave aerials then used to move telecommunications traffic from London to the rest of the country, as part of the GPO microwave network. It replaced a shorter steel lattice tower of the 1940s on the roof of the Museum Telephone Exchange, so named for its closeness to the British Museum; a taller structure was needed to protect the radio links' line of sight against tall buildings then planned in London. The links ran by way of GPO microwave stations at Harrow Weald, Bagshot, Kelvedon Hatch and Fairseat, and locations including the London Air Traffic Control Centre. On completion the building was known as the Museum Radio Tower, after the exchange next door.

The design came from the Ministry of Public Building and Works under its chief architects Eric Bedford and G R Yeats. Concrete clad in glass, the narrow cylindrical shape was chosen to give the aerials a stable platform, and the glass cladding had to be tinted to prevent overheating. The tower had originally been designed at just 111 metres; as built, the main structure stands 177 metres high, with aerial rigging bringing the total to 189 metres.

Construction began in June 1961, with Peter Lind & Company as main contractor, and had reached 475 feet by August 1963. A tower crane jib sat across the top for virtually the whole build, and in August 1963 the question of its removal was raised in Parliament: Reginald Bennett MP asked the Minister of Public Buildings and Works, Geoffrey Rippon, how he proposed to take the crane down once it had served its purpose, and Rippon replied that "this is a matter for the contractors" and that "there appears to be no danger of the crane having to be left in situ". Rippon topped the tower out on 15 July 1964. The revolving restaurant was prefabricated by Ransomes & Rapier and the lattice tower by Tubewrights, a Stewarts & Lloyds subsidiary; much of the telecommunications equipment was made by GEC, and the construction cost was £2.5 million. An Act of Parliament passed in the 1960s varied the fire regulations so that the building could be evacuated using its lifts, unlike other buildings of the time.

The first microwave link, to Norwich, opened on 1 January 1965, and Prime Minister Harold Wilson inaugurated the tower on 8 October that year. The Met Office put a weather radar on the top. The public opening followed on 19 May 1966 and was performed by the Postmaster General, Anthony Wedgwood Benn, and by Billy Butlin; Queen Elizabeth II had visited two days earlier, on 17 May.

Alongside the communications equipment and office space there were viewing galleries and a souvenir shop, and Butlins ran the Top of the Tower revolving restaurant on the 34th floor, which made one revolution every 23 minutes and served meals at about £4. In the first year the tower drew nearly a million visitors and over 100,000 diners.

A bomb exploded in the ceiling of the men's toilets at the Top of the Tower restaurant at 04:30 on 31 October 1971, and the blast damaged buildings and cars up to 400 yards away. Responsibility was claimed by members of the Angry Brigade, a far-left anarchist collective; a call was also made by a person claiming to be the Kilburn Battalion of the IRA.

The tower was closed to visits by the general public after the bombing, though the restaurant reopened. Butlins managed it until the lease expired in 1980. That was also the year the building ceased to be the tallest structure in London, which it had been since its completion.

Information about the tower was designated an official secret, and in 1978 the journalist Duncan Campbell was tried for collecting information about such locations; the judge ordered that the tower could be referred to only as "Location 23". An urban legend held that it had been left off Ordnance Survey maps of London until the 1990s, despite being a 177-metre structure in the middle of central London that had once been open to the public. The MP Kate Hoey cited the story in Parliament in 1993 as an example of "seemingly trivial information that remains officially secret", using parliamentary privilege to state that "the British Telecom tower does exist and that its address is 60 Cleveland Street, London". The tower can in fact be found on Ordnance Survey maps from before that time.

Successive changes of ownership carried the building through the names Post Office Tower and Telecom Tower before it took its present name in 1991. Its microwave aerials remained in use into the 21st century, by then connected to subterranean optical fibre links. Historic England designated the tower a Grade II listed building in 2003, and the listing covered several of the defunct antennae attached to it, meaning they could not be removed unless listed building consent was granted; permission was given in 2011 on safety grounds, the antennae being in a bad state of repair with fixings no longer secure, and the last of them was taken down in December 2011.

From 2006 the tower was used for short-term air-quality observations by the UK Centre for Ecology & Hydrology, work that has continued in more permanent form as the BT Tower Observatory, monitoring pollution and greenhouse gases above ground level in order to determine their sources. The National Centre for Atmospheric Science takes NOx measurements there and has quantified the effect of the ULEZ on air quality.

In 2009 a 360-degree coloured screen of 529,750 LEDs was installed 167 metres up, across the 36th and 37th floors, replacing an earlier light projection system; it was then the largest of its type in the world. It displayed a countdown of the days remaining until the start of the 2012 Summer Olympics, and in April 2019 it broadcast a Windows 7 error message for almost a day. The Times reported in October 2009 that the revolving restaurant would reopen in time for the 2012 London Olympics, but by December 2010 those plans had been "quietly dropped". The revolving floor is still there, and the tower has been used for events including a children's Christmas party and Children in Need in 2010; for its 50th anniversary the 34th floor was opened for three days, from 3 to 5 October 2015, to 2,400 winners of a lottery. On 21 February 2024 BT Group announced the sale of the tower to MCR Hotels, who planned to retain it as a hotel.