The GPO, Post Office Telephones and British Telecom (BT)

This page documents the Cold War infrastructure of the UK state telecommunications operator the GPO the predecessor of the now private limited company British Telecom. Descriptions of the services to support cold war communications may be found in other topics on this site.


At the start of the Cold War the General Post Office (GPO) operated all UK telecommunications. The GPO was a Government department with its finances strictly controlled by the treasury. In October 1969 the Post Office ceased to be a Government department and became a pubic corporation. The letter and parcel business became Royal Mail and the telecommunications arm became Post Office Telephones. In 1981 the British Telecommunications Act separated the services of the Post Office and Post Office Telephones became the public corporation British Telecom (BT). The Government privatised BT in November 1984 whilst still retaining a controlling share in the new company. The term BT is used throughout this site to mean British Telecom PLC and its predecessors.

In the 1960's and early 70's the UK telecommunications infrastructure was very different from today's modern networks. Telephones were a luxury item with less than 50% of households owning one. All telephones were fixed landlines with a handful of very costly vehicle based mobiles operating close to major cities. The network was exclusively run by the Post Office. As a Government department the Post Office had been starved of money by the exchequer. There were long waiting lists and a shortage of lines forced many people to accept party lines. Two houses would share the same wires to the exchange in a party line. Although they had different numbers there was no privacy between parties. The lack of lines meant users would encounter the engaged signal and there were even television adverts discouraging the use of the telephone.

It was not until 1982 that other companies were allowed to provide telephone services. Mercury Communications were the first to provide an alternative. They provided the backbone for many of the emerging cable television companies who began to provide business and residential telephone lines in the area they cabled. The Mercury network only connected major centres in a figure of eight and was very reliant on BT to deliver the final leg to the customer. As this wasn't a truly independent network, the majority if not all the civil defence communications remained in BT's hands.

UK Land Line Communications

Until telecommunications liberalisation the 1980's BT had almost exclusive rights to provide landline based communications systems. They ran the whole of the public telephone system. A separate public teleprinter network known as TELEX, now closed. Operated their own private teleprinter network for sending Telegrams between telegraph offices, now closed. Although some large companies had their own internal telephone systems they were forced to use BT lines (Private Circuits) to connect between offices. A private circuit ( known as a Leased Line in some countries ) meant the renter had exclusive use of the wires provided to their premises by BT. It made sense that BT would provide all landline based Military and Civil Defence communications too. Television pictures were carried on BT cables or microwave links from studios to transmitter sites.

BT Microwave System for the Cold War

Austrey Microwave Relay Station

Austrey Microwave Station

In the early 1960ís the Post Office as it was then built a microwave network consisting of chains of concrete or lattice towers across the countryside every 30 miles or so. The London 'Post Office Tower' now known as the 'BT Towerí being the one familiar to most people. At the time of its construction microwave links each carrying 960 telephone channels offered a cost effective alternative to laying long distance copper cables.

Horn Aerial

Microwave Horn Aerial

Over the years there has been much speculation of the purpose of the microwave system. It certainly was used for carrying Television, Telephone and Private circuits over long distances. However some authors have suggested devious military or spying purposes which seems unlikely. The web site dedicated to Cold War buildings which is linked from this site carries an account of the 'Backbone Microwave Towers' which I believe to be accurate. The Emergency Wartime Government Emergency HeadQuarters (EWGHQ) 'Burlington' an underground complex in former stone quarries near Hawthorn on the western outskirts of Corsham was connected into the backbone network at Fiveways microwave tower.

When the towers were originally built microwave horn aerials were used. Horns were technically difficult to use as the feeder waveguide had to drop down vertically as bends in waveguides had to be avoided. As the network capacity grew these were supplemented by numerous dish aerials working on many different microwave radio frequencies. Microwaves links are limited in length by the curvature of the earth as the aerials must be in line of sight. The signals are affected by weather conditions and reflections from water if they cross the sea causing fading. To overcome fading two dishes would be used and spaced a distance apart so they were affected differently. At the receiver the strongest signal could be selected at any instance of time.

Part of the 1970's Network

UK 1970's Microwave Network

In my apprenticeship notebook I recorded the documented microwave links that didnít appear to go to television stations. Unwittingly I had recorded the 1970's network for the 'Master Radar Stations' as they were known at the time. These video links allowed operators at one radar station to monitor other sites to see a national picture. The drawing of the network shown here shows only the terminal microwave stations. These were the places the microwave bearers were broken down into their component parts. Terminal stations were linked together via a number of relay stations such as Austrey which simply forwarded the whole group of channels without breaking them down. To create a video link between Staxton Radar and Neatishead Radar, a link from RAF Staxton to BT Cave Wold terminal station would be connected end to end with a link from BT Cave Wold to BT Morborne Hill and a further link from BT Morborne Hill terminal station to RAF Neatishead. The network shown was superseded many years ago as the UK Radar stations changed.

Burlington EWGHQ [1984]

Fiveways mast serving Burlington

The original microwave network was expanded over the years reaching maturity in the early eighties. A while ago the original horn aerials were removed. But prior to their removal they provided a good indicator that the tower was one of the original sites from the 'Backbone' era.

At the time of writing this page (2009) most of the long haul microwave dishes are being removed from the BT microwave towers leaving some looking very bare. Optical fibre cables now provide the long distance lines with a huge bandwidth that could not be achieved with microwave links.

Secret Underground Exchanges

Three underground exchanges were built in the 1950ís that were classified until the 1960's. These were designed to withstand a Hiroshima type blast but as atomic weapons became more powerful they were rendered useless. The exchanges were used until the early 1980ís but now only the cable infrastructure remains.

The largest was 'London Kingsway' which BT has been trying to sell recently. A good account of London Kingsway following its history from WW2 to present day may be found at that is linked from this site.

The 'Manchester Guardian' exchange came to the public notice in 29 March 2004 when a fire in the cable network severely disrupted the telephone network around the Manchester area.

For a time the 'Birmingham Anchor' exchange and cable tunnels had been declared unsafe to work in due to water seepage. But BT has recently refurbished them to make them safe again as they now carry underground cables across the city.

Anchor Exchange

Click the thumbnail to watch the 1998 BBC video of Birmingham Anchor on YouTube

Birmingham Anchor Exchange (BM/AN) is underneath Telephone House in Newhall Street. The exchange Strowger switching equipment and repeater station were in two large tunnels on two levels, other large tunnels contained the standby generators and air conditioning plant. A smaller diameter cable tunnel runs South and connects with Midland Exchange and ended near the corner of Essex St and Bromsgrove St. This had access from the BT Essex St stores complex, now redeveloped as flats. Before the tunnels became unsafe some of my planning colleagues would walk through them between Midland exchange and Telephone House to avoid getting wet on a rainy day. A Northward tunnel was planned to connect to a point at the rear of Hockley Sorting Office, however this apparently was never completed.

Other sources on the web falsely suggest it was possible to walk to Smallbrook and Aston Cross exchanges. A series of deep level cable tunnels exist around the city but do not give access to those exchanges. Another falsehood on the web, is the assertion the basement of Aston University was connected into the cable tunnels. The tunnel approaching Aston Exchange and the University ends outside the 'W i l l i a m   B o o t h   C e n t r e' in Shadwell Street.

This BBC video on YouTube shows plenty of detail in a quick tour of the Anchor tunnel system but wrongly suggests it was the Midlands Regional Seat of Government, that was actually, RGHQ 9.2 Drakelow. Nevertheless it was an important place for telecommunications in the Midlands with circuits extending all over the area.

There are a few visible signs of the Anchor tunnels on the surface. Air Vents and Lift Access points can be seen next to the Telephone House in Fleet Street and also Lionel Street goods lift access. The Church Street lift is hidden at street level but can be distinguished on the aerial photograph. The staff entrance lift is in Telephone House. At the time of the construction of Anchor, Telephone House contained a local telephone exchange known as 'Central' and two trunk exchanges 'Newhall' and 'Colmore Lodge' all using Strowger switching equipment. Anchor's Strowger switches were removed in the early eighties. By 1995 the Digital Network had completely replaced all Strowger and electronic / transistorised analogue switches throughout the country.

Hardened Repeater Stations

The connection between the home telephone and the exchange is carried on a single pair of wires. Over the relatively short distances involved, it is economical to bundle these together in large cables, some containing as many as 2000 wires. Over long distances, the use of large cables is not economic. A system of multiplexing 24 analogue speech channels into two pairs of wires was developed. Further developments increased this capacity. By the 1970's a 4MHz co-axial cable could carry 960 channels on two coax tubes, one for each direction of speech. Today 40GB optical fibres have 10,000 times this capacity.

When a single telephone call is sent down a long pair of wires between exchanges, it must be amplified at regular intervals. The amplifying point is called a Telephone Repeater Station (TRS). Most large Automatic Telephone Exchange (ATE) buildings incorporated a TRS too. In small exchanges a special area wasn't warranted for the TRS so the amplifier racks were placed alongside the switching apparatus. On long distance routes, the multiplex equipment at each end was housed in the repeater station rather than the exchange part of the building. Coax cables carrying television or multiplexed speech channels required amplifying every couple of miles. Where no suitable exchange building existed, a repeater station in a small brick building the size of a garden shed was built.

At some locations such as Rothwell Haigh in Yorkshire, special hardened repeaters stations were built to house the repeater equipment. This particular building served a now disused RAF communications centre and has been sold off.

A two storey semi-sunken hardened repeater station was constructed in 1954 on the Coventry Road, Sheldon a suburb on the East side of Birmingham. Map reference SP141842. Known as Lyndon Green, it was contemporary with the secret underground exchange in Birmingham City centre. At the end of its cold war use the building served as the Regional repair workshop during the 1980's - 90's. In the gallery there are pictures of the property taken in March 2009. The hardened concrete core has brick built offices attached.

A similar hardened repeater station was built at Whitecroft Road, Queslett a Northern suburb of Birmingham. Map reference SP051943 and now houses the 'Beacon' telephone exchange.