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GCHQ - Government Communications Headquarters

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A GCHQ officer on surveillance

The Government Communications Headquarters is a part of the British intelligence community. Working closely with MI5,1 and MI62. Like MI5, GCHQ is a Civil Service department. Its main 'customers' are the MoD (Ministry of Defence), law enforcement agencies and the Foreign and Commonwealth Office, although it also serves a wide range of other government bodies.


In the summer of 1939, a few cipher experts arrived at Bletchley Park, in Buckinghamshire, England. Bletchley Park was the home of GC&CS3 (later to become GCHQ) the main job of these experts was to break the Enigma Code.


The chances of breaking the code if you didn't know the settings were somewhere in the region of 150,000,000,000,000,000,000 (that's 150 million million million) to one. But the experts at GC&CS had a few advantages; through information passed on by their contacts in Poland, they knew of a design flaw that meant that no single letter of the alphabet could be encrypted as itself. Also with the help of captured information4 they could use 'cribs'. A crib is a piece of encoded text whose meaning is known or can be guessed; the Germans always started their messages off with a piece of standard information, such as a description of the weather.

Even with a known crib in an encoded message, thousands of possible Enigma settings had to be checked in order to crack to the code. This is where a famous mathematician by the name of Alan Turing comes in. He designed an electro-mechanical machine called a 'Bombe' - so called because of its constant ticking. Each Bombe could simulate the settings of ten enigma machines at high speed. It was thanks to these machines that the British could decipher most of Germany's secret messages and avoid U-boat attacks in the Atlantic, know of bombing raids before they happened, and track the deployment of German troops across Europe.


Another code that was broken at Bletchley Park was a very sophisticated cipher used by the German high command called 'Lorenz'. Although GC&CS had broke the code it still took weeks to decipher the individual messages, by which time it was often too late. Enter Max Newman and Tommy Flowers who designed a computing machine called Colossus; this was the world's first programmable electronic computer. It was the size of a small living room, weighed in at about a ton (about 0.984 metric tonnes) and it had 2400 valves, (which have been replaced in modern computers with the transistor). This computer remained a huge secret for years, and it is due to this that two Americans were credited with inventing the first electronic computer in 1945. Colossus, however, was first and proved to be an invaluable tool in the preparation for D-Day.

The End of the Bletchley Code-breakers

It is estimated that during WWII GC&CS employed around 10,000 staff - these people helped shape the course of the war in Europe and may even have shortened it. In March 1946, GC&CS moved to Eastcote, London and was renamed GCHQ.


Early on in World War II, the War Office5 bought land at Benhall and Oakley farms (Benhall was to the west of Cheltenham and Oakley to the east) on which they quickly built temporary offices which were used to house units evacuated from London. In 1942 these were taken over by the American Army who used them as a logistics base. After D-Day, this American unit moved into France and it is not known exactly what the sites were used for. In 1946 the sites were used to retrain ex-forces and other war workers for civilian life.

Although GCHQ had moved back to London, it was in temporary lodgings; it was decided that a long-term home would be needed for GCHQ away from London, so it didn't have to keep moving at times of war. The Cotswolds6 were looked at in general, and it was a chance visit in 1947 by a member of GCHQ that led to the discovery of the site at Benhall, which was about to be abandoned. In 1949 it was decided that GCHQ would move to Cheltenham. The government, however, had a problem.

Housing in Cheltenham was thin on the ground, so the government had to build housing for the staff being moved from Eastcote to Cheltenham; this was done between 1951 and 1953 after much wrangling with the local council. It was first thought that the original buildings at Benhall and Oakley would be adequate, but it was soon discovered this wasn't the case, so additional office space and workshops were built at both sites. This was completed in 1954 and GCHQ now had its new permanent home.

Public Key Encryption

Originally all encoded messages relied on both the sender and the recipient having the same 'key' to decode the message. This caused huge problems, because the key had to be distributed to senders and recipients, and could be intercepted or 'sold' to the enemy. The British military presented this problem to GCHQ in 1973 and they came up with a solution we now know as public key encryption.

Basically one 'key', which is widely available to senders (ie a public key), is used to encrypt a message, but the recipient has a different 'key' which deciphers the message. This way anybody can encrypt a message with his or her 'key', but the same 'key' won't decipher any messages. This is now used on the Internet for secure transactions. In 1977, a group of Americans invented the same method, and, as with Colossus, they were credited with its invention. However, GCHQ had accomplished this years before.

Trade Unions

In the late 1970s, the British economy was in trouble, with inflation reaching levels of 25%. The government tried to control this by imposing pay restrictions within the civil service. This caused strikes across the board, and GCHQ also had internal disputes between management and other staff.

From the government's point of view, any industrial action taken by GCHQ staff would mean the organisation wasn't working as effectively and therefore this would compromise national security. It was felt that the unions that expected their members to take action were indeed being irresponsible.

On the 25 January, 1984, the government announced changes to the conditions of service for GCHQ staff, these changes meant that they could no longer be a member of trade unions, and to compensate for their loss of statutory rights they would be paid £1000. These changes were to take place at the end of March that same year; staff who didn't want to accept these changes were offered transfers to different civil service departments or had to leave the civil service altogether.

In the end 98% of GCHQ staff accepted these new changes7, however a few legal cases were fought out (the last ending in 1987) and the last 14 members who would not give up their trade union rights were dismissed. There were annual rallies held every January from 1985 to 1997 in Cheltenham over the trade union bans.

Following the 1997 general election (in which the Labour party came into power), the Foreign Secretary, Robin Cook, announced that these restrictions would be lifted and arrangements for compensation made. The first of those who had been dismissed from GCHQ returned on the 9 September, 1997.


GCHQ is still based in Cheltenham today, and continues in the same role as before, which can be broken in to two main areas.


Nowadays the technology used by Signals Intelligence, or Sigint for short, is a far cry from the old days of trying to crack codes (although this is still a function). In modern peacetime, GCHQ provides central government with information, which is then used in the fields of national security, law enforcement and during war military operations. This information is of great help in the prevention of terrorism of other serious crime.

Information Assurance

It is this aspect of GCHQ's role that brought us Public Key Encryption. The main aspect of information assurance is to ensure the safety of all government information - this might be government computer networks or it could be lines of communication. GCHQ also helps to protect the computer networks of the country's infrastructure, eg electricity, water etc.


The NSA (National Security Agency) is the USA's answer to GCHQ, only on a larger scale. Quite often, the NSA and GCHQ share information they gather and/or technology they develop, if it is in the interest of both nations.

On the Move Again

GCHQ is about to move again; it is staying in Cheltenham but is moving in to a purpose-built site on the original Benhall site. This building has been nicknamed the 'Doughnut' because of its shape, and has featured in the news in recent years due to it being grossly over-budget and over-schedule. Currently the move is due to be completed in 2003.

Finding Out More

1Also called The Security Service, it is charged with security within the British Isles.2Or British Intelligence, made famous by James Bond.3Government Code and Cipher School.4Despite what Hollywood might have you believe, this information was captured by the British Royal Navy.5Now the MoD.6An area of western England between Bristol and Birmingham.7Only 40% of staff were union members anyway.

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