BT (Post Office) Tower (1964) : the best view in town
Now called the BT Tower, this is one of London's most famous landmarks, soaring above the skyline in the city centre. However it was built purely for practical reasons.
During the 1950s, the volume of calls was expanding rapidly. At the same time microwave links became a more cost-effective proposition than cables for distributing television programmes along with the growing volume of telephone call traffic. The problem was that new tall buildings being constructed in London were blocking the transmission path of the radio links.
The Post Office decided the best way to resolve the problem was to build something so tall that nothing would obstruct its line of sight.
Construction of the 580 foot tower began in 1961 and was completed in July 1964. The Tower was opened for business by the Prime Minister on October 8, 1965, once all the equipment had been fully installed.
Although packed with the latest technology, its chief interest to the public was as the tallest building in London with its observation room and revolving restaurant. Following a terrorist bomb incident in 1971 the public viewing gallery was closed and only the restaurant remained open, finally closing in 1980.
B1 standard building & Unit Automatic Exchange (1950s) : off the peg
This building was an actual working exchange that was moved lock, stock and barrel from its working location in Essex to the Avoncroft Museum for preservation.
It's a typical example of the type of exchange in use at the time. Buildings were constructed virtually off the peg. They came in different sizes and materials, wood, brick or stone, chosen to fit the location and budget. This B1 wooden construction replaced a smaller exchange, as demand increased in the area.
The Unit Automatic Exchange was created in a similar way. It came in different sizes according to the number of telephone users to be served - 200, 400, 600 etc. This example, the UAX 13, could have served a maximum of 800 connections.
Central Telegraph Office, London (1874) : the home of the telegraph
London's Central Telegraph Office (CTO) played a key role in the development of modern telecommunications. In its heyday this was the largest telegraph office in the world, which communicated directly with every major town in the UK.
It moved to a building in Newgate Street known as General Post Office (West) in 1874. By the end of the century its 4,500 clerks were dealing with 150,000 messages every day.
The CTO was a prime target for German bombs in both world wars and in 1940 it was virtually destroyed by fire. Although the building was rebuilt after the war, most of the telegraph work was transferred to other places.
As telephone and Telex messages began to replace the telegram, the CTO went into decline. It was finally demolished in 1967.
In 1979 planning permission was given to build a new office on the Newgate Street site. The British Telecom Centre opened in 1984 and became the company's headquarters.
Epsom Telephone Exchange (1912) : making a direct connection
In 1912 The Post Office installed Britain's first automatic (dial) telephone exchange at Epsom. The equipment was new and needed thorough testing. Epsom was ideal as the exchange saw heavy surges of calls on racing days. The town was also close enough to London for technical and administrative staff to monitor its performance.
Epsom was installed with 'Strowger' two-wire type equipment, which later became the UK standard. The exchange was equipped to handle 500 lines and for the first time users could make a call without having to speak to the operator first.
Curiously the Epsom exchange did not remain automatic. New customers eventually exhausted the original equipment's capacity in 1932, when the most economic replacement was a manually operated exchange.
Faraday Building : the citadel of the city
In the 1930s and 1940s the Faraday Building complex was the centre of Britain's telephone network, with circuits radiating to nearly every other system in the world.
The GPO had opened its first London telephone exchange on the fourth floor of a building here in 1902. Five years later, a second exchange was added to cope with rapidly increasing demand.
Faraday became the central switching centre for the whole of London. It was a vital communications point and a prime target as well, so in 1940 the north-east part of the building was constructed in a fortress-like structure, known as the 'Citadel'.
With the upgrade to digital technology during the 1980s, the Faraday Building soon became outdated, its switching role taken by Mondial House. However, Faraday Building has continued to be a major telecommunications building, and looks likely to remain so for many years to come.
Mondial House (1980) : giving the city a better future
Mondial House was the result of a visionary concept developed in the 1970s to create the largest international switching centre in the UK.
The building was designed futuristically, with state-of-the-art concrete and white plastic cladding surrounding a huge building of 57,000 square metres. It stands next to Cannon Street station in the centre of London's financial quarter.
Mondial House was planned to hold a complete range of switching equipment, repeater stations, cable terminations, mains power generation, operator centres, staff and training facilities, but by the time the building was finally equipped in the mid-to-late 1980s, some of the earlier technology had become outdated and an overhaul was needed immediately. The old equipment was stripped out and Mondial was installed with computer control and electronic accounting to oversee a mix of analogue and digital technologies.
Mondial House closed as an operational BT building on December 31 2004.