F Branch was MI5’s domestic counter-subversion branch and therefore the department that had the most direct contact with the Special Demonstration Squad (SDS) and the other relevant squads within Special Branch.
In 1953, F Branch had responsibility for ‘counter-subversion at home’. MI5’s interest in subversion was rooted in the Cold War, although, prior to decolonisation, activities undermining the British Empire were also termed ‘subversive’.
Appearing at the Undercover Policing Inquiry on 22 March 2021, a senior Security Services manager known as Witness Z explained how relationships evolved between F Branch and the SDS.
Witness Z described a relationship that developed from relatively irregular contact through F4 in the late 1960s into a more regular liaison by F6 by the late 1970s, with F7 requesting SDS undercovers to target specific groups and events. MI5 also occasionally asked the SDS to identify potential civilian informers for MI5 to recruit.
In 1988, the FX Branch that handled counter-terrorism was renamed G Branch. The rest of F Branch was incorporated into MI5 C Branch at around the same time. In 1994, with the Cold War over, MI5 reduced its interest in subversion to a ‘watching brief’.
Unless stated otherwise, the source is the written statement that Witness Z provided on behalf of MI5 (The Security Service). Additional detail comes from Christopher Andrew’s authorised history of MI5. Also, the unauthorised: The Silent Conspiracy: Inside the Intelligence Services in the 1990s, by Stephen Dorrill has also been utilised.
F Branch and its sections
Overview
F Branch was MI5’s principal domestic counter-subversion branch and therefore the department with most direct contact with the Special Demonstration Squad (SDS) and Special Branch.
Witness Z described a relationship that developed from relatively irregular contact through F4 in the late 1960s into a more regular liaison by the late 1970s through F6, with F7 setting many of the substantive intelligence requirements.
It is worth noting that subsections, known as ‘desks’, have appeared, disappeared and had changing remits across MI5’s history.
F Branch role and structure
In 1968 F Branch’s function was described as ‘Counter-subversion home’. By 1976 the organisation chart divided its responsibilities between F, counter-subversion, and FX, counter-terrorism.
F Branch had primary responsibility for MI5’s liaison with both the Metropolitan Police Special Branch (MPSB) and provincial Special Branches. Even A Branch’s liaison with MPSB over surveillance had to be conducted through, or approved by, F Branch.
F Branch sections
Section | Function and source comparison |
|---|---|
F1 | Witness Z did not define F1’s precise remit, but Christopher Andrew has describes it being responsible for investigating the Communist Party of Great Britain (CPGB). Witness Z noted that senior F1 officers liaised with MPSB. |
F1A | This designation was probably used in the 1950s for the ‘study group’ that identified Communist Party members and trained new MI5 officers. In 1975, F1A was tasked with a wide-ranging investigation of subversion in the Labour Party. F1A also reported in April 1982 on the rapid expansion of the Campaign for Nuclear Disarmament (CND). |
| F1A/1 | Sub-desk of F1A |
F1A/9 | F1A/9 wrote nine papers on the Militant Tendency over two years to January 1978. |
F1B | A full-time desk for Irish security, focusing particularly on Northern Ireland, was established in F1B in spring 1969. By autumn 1969, it consisted of a female assistant officer supported by Stella Rimington. |
F1C | In spring 1969, Irish matters were still handled by one part-time F1C desk officer. It also says that, at another point, F1C became the designation of the Communist Party ‘study group’, replacing F2C. This shows that the same subsection labels could serve different functions at different times. |
F2 | According to writer Stephen Dorril, F2’s role in the early 1980s was to investigate trade unions, producing Box 500 reports for the Whitehall committees and working closely with the Civil Contingencies Unit during strikes. Separately, Witness Z assigned particular ideological targets to F2B and F2C. |
F2A | F2A monitored the CPGB during the Second World War. |
F2B | Witness Z said F2B dealt with Trotskyist organisations, including the Militant Tendency and Socialist Workers Party. |
F2C | From 1968-1983, Witness Z said, F2C investigated communists, anarchists and the extreme right wing. |
F2N | This unit dealt with trade unions, according to Stephen Dorril, between 1981-1983. |
F2R | This unit dealt with the media, education and Members of Parliament, again according to Stephen Dorril. |
F2R/1 | A subdivision of F2R whose responsibilities around 1984 included monitoring alleged subversion in the peace movement. |
F3 | Witness Z said F3 took over E Branch’s work after its abolition in 1971 and investigated the international dimension of subversion. |
F4 | Witness Z said F4 was responsible for running counter-subversion agents. It coordinated agent coverage with Special Branch and sought to prevent duplication. |
F5 | Irish terrorism, particularly loyalism, according to Stephen Dorril. |
F6 | Witness Z said F6 was created in January 1974 to coordinate joint coverage of subversive groups and individuals. It became the principal section managing MI5’s relationship with the SDS, receiving and distributing reports and coordinating targeting and feedback. |
F6 Ultra-Left subsection | A subsection of F6 dealing with the ‘ultra-left’. By July 1981, it worked in close liaison with the SDS and participated in monthly targeting meetings. |
F7 | Witness Z said F7 was created in July 1976 and was primarily responsible for Trotskyist, anarchist, and right-wing organisations. |
F8 | F8 served as the London headquarters for MI5’s Belfast station after the Irish Joint Section was wound up in 1984. It tentatively identified the agent-running section headed by the officer ciphered G/02 in the de Silva report as probably F8. |
FX | Witness Z’s 1976 chart identified FX as counter-terrorism and recorded ‘Director F and FX’ participating in 1977 discussions with MPSB. |