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

This topic has been revised during 2016, thanks to Dan Glover sharing his information with me as he researched into the BT Archives during the preparation of his website. [link to be added when it is live] 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. One rather stupid idea put forward was the microwave beams being intercepted at Regional Government Headquarters at times of war.

The conspiracy theories have been fuelled by a GPO paper in the National Archives [CAB 134/1207] dated 1956 proposing a microwave backbone bypassing major cities to safeguard vital communications at times of war. However, during the late fifties and early sixties the demand for long distance television links outstripped the provision of coaxial cables, the early growth of the microwave links was for television not the cold war. This wasn't a network but separate point to point microwave links patched together where the preferred option of coaxial cables did not or could not be provided in time to meet the broadcasters demands.

Only later on did a long haul network form. Modernisation of the highlands and islands telephone system in the seventies relied on microwaves to provide connections to local exchanges, but this wasn't part of the national long haul network characterised by 3 or 4 metre dishes on tall towers. The national network continued to grow for a number of years reaching maturity in the early eighties.

When Optical Fibre made its way into the BT network providing huge capacity for telephony and especially the growing data market. The relatively low bandwidth long haul microwave network became redundant. During the mid-2000's the long haul microwave dishes were removed from the BT microwave towers leaving some looking very bare. Only those serving the highlands of Scotland still remain. Microwaves are still used to feed some medium bandwidth customers premises, but with the drive to provide fibre to the customer, their life expectancy is rather short.

Mr L.R.N. Mills former head of PO Inland Radio Planning, writing for Connected Earth - Birth of the BT Tower sums up the position in the early sixties : . . . Thus we had a number of disjointed radio links connected together by cable with no apparent plan for a national radio network. Then came Backbone, a system planned to provide secure communications between strategic Government locations avoiding cables which, by the very nature of the network, passed through important towns and cities. The Backbone network deliberately avoided built-up areas and thus did not provide any basis for a national city to city radio network. Top management in the Radio Branch were somewhat irritated by this. . .
. . . Then came, BBC2, 625-line colour television. . . plans were at last laid for a national city to city microwave radio network. . .
Next question, if a national radio network were established for TV, would adding telephony channels to radio links be cheaper than laying more cables? [Yes] . . .
. . . The conclusion from all this is that we have mainly to thank the coming of 625-line colour television for the existence of BT's microwave radio network and the [London] BT Tower.
and he should know.

Horn Aerial

Microwave Horn Aerial

The early parts of the network used microwave dish aerials. Later on microwave horn aerials became the norm as they could provide dual polarisation and dual band working for increased capacity. Developments in dish aerials design allowed their use to become widespread and eventually most of the bulky and heavy horn aerials were replaced by dishes.

Microwaves links are limited in length by the curvature of the earth as the aerials must be in line of sight of each other. This dictates the spacing of microwave stations and the height of towers. The signals are affected by weather conditions and reflections from water if they cross the sea, causing fading. To overcome fading two dishes spaced a distance apart so they are affected differently by the changing condition are connected to the receiver which selects the strongest signal at any instance of time.

Some authors have wrongly associated the microwave backbone with the ROTOR radar plan of the early fifties. This can be discredited as ROTOR was a low bandwidth system not needing microwave links and preceded the first mention of plans for backbone.

UK defence policy was rather fluid to say the least. ROTOR 1 was superseded by the '1958 Project' which in turn was rehashed as 'Plan Ahead'. This later became 'Linesman Mediator' a combined air defence 'Linesman' and civilian air traffic control 'Mediator'. By now we are in the mid nineteen sixties.

The GPO microwave system was used to provide the video links for 'Linesman Mediator' radar, these are recorded in the BT Archives in a PO document dated Sep 1966.

Part of the 1970's Radar Links

Radar Station Links

Neatishead - Staxton Wold (expected RFS May 1967)
Neatishead - West Drayton (June 1967)
Staxton Wold - West Drayton (August 1967)
Dundonald - Boulmer (March 1967 - see note [1])
Boulmer - West Drayton (August 1967)
Boulmer - Staxton Wold (in-service but modifications needed October 1966 completion)
Staxton Wold - Patrington (January 1968 - see note [2])
Killard Point - West Drayton ( November 1968) (Killard Point aka Bishops Court)

[1] Dependent on Craiglockhart site and Wooler permanent building
[2] Dependent on Hornsea site

In my apprenticeship notebook I recorded the documented microwave links between terminal radio stations ( RS ) that did not appear to go to television transmitter sites. Unwittingly I had recorded most of the seventies network for the 'Master Radar Stations' as they were known at the time corresponding to the archive material. These video links allowed operators West Drayton and those at one radar station to monitor other sites to see a national radar picture.

My drawing of the network 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 similar to 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 Cave Wold RS terminal station would be connected end to end with a link from Cave Wold RS to Morborne Hill RS and a further link from Morborne Hill RS terminal station to RAF Neatishead. It is entirely possible to make parts of connection by co-axial cable too. The network shown here was superseded long ago.

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 (circa 2010) refurbished them to make them safe again as they 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 from view 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 underground Anchor Strowger Exchange, above ground 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. The one at Warmley near Bristol once handled circuits from the Central Government 'Burlington' bunker, but has long since been demolished.

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.