The House of Lords Library briefing has been produced to mark GCHQ’s 100th anniversary.
GCHQ: 100th Anniversary (183 KB , PDF)
On 1 November 2019, the Government Communications Headquarters, widely known as GCHQ, reaches its 100th anniversary. This briefing provides a brief overview of its history and its role today.
GCHQ came into being in 1919 following the end of the First World War. The Government had deemed the British Signals and Intelligence unit, which had intercepted German radio traffic throughout the war, so valuable that it formed a peacetime cryptanalytic unit to continue its work. Originally called the Government Code and Cypher School, the unit was formed on 1 November 1919.
In the interwar years, the Government Code and Cypher School had the overt function of protecting British Government communications and a secret mission to decrypt messages sent by foreign countries. However, a GCHQ profile of Alastair Denniston, its director between 1919 and 1942, has claimed the constraints which the Government Code and Cypher School operated under during the interwar years were “more damaging than anybody realised”.
Towards the end of the 1930s, work began to prepare the Government Code and Cypher School for the possibility of war. In August 1939, almost all the staff were moved to Bletchley Park and the Government Code and Cypher School started to call itself GCHQ, short for Government Communications Headquarters. The operation at Bletchley Park has been seen as central to the Allies’ success and credited with saving thousands of Allied lives in the war.
During the Cold War, the signals intelligence (‘sigint’) produced by GCHQ constituted most of the secret information available to political decision makers, according to author Richard J Aldrich. At the end of the Cold War, GCHQ was a potential target for funding cuts. However, conflicts in Bosnia and Kosovo demonstrated the ongoing value of sigint. In the 1990s, the Government made plans to expand GCHQ. In 2003, the organisation moved into a new headquarters, however, the events of 9/11 meant the building was already deemed too small.
Today, GCHQ describes its modern mission as much more diverse than when it was formed. It says “supporting the military is still very much part of our role but we also now tackle the most serious cyber, terrorist, criminal, and state threats”.
GCHQ: 100th Anniversary (183 KB , PDF)
The ‘Strategic defence review 2025’ (SDR) was published on 2 June 2025. Contending that the UK faces a generational defence and security challenge, the SDR makes 62 recommendations across the armed forces and wider society to meet this threat. The government has pledged to implement all those recommendations. However, critics question where the resources to meet the requirements of the SDR will come from, despite government pledges to raise defence spending levels.
The Chagos Archipelago has been the subject of a long-standing dispute over its sovereignty between the UK and Mauritius. Having been retained by the UK since 1965, the largest island, Diego Garcia, later became the site of a joint UK-US military base. In May 2025, the UK reached an agreement to transfer sovereignty of the islands back to Mauritius, while maintaining an initial 99-year lease of Diego Garcia. The agreement also includes security and financial provisions.
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