Utilising a new documentary source, namely correspondence between A. K. Chesterton (1899–1973), one of the most important figures of the post-war far right in Britain, and H. J. van den Bergh (1914–1997), the head of the South African Bureau of State Security (BOSS), this article presents a case study that leads to an enhanced understanding of the nature and workings of the overseas activities of the South African security apparatus during the 1960s, its allies and its targets. The article examines and evaluates the evidence presented in this correspondence regarding the covert operations of the South African secret services against anti-apartheid activists and other exiled ‘subversives’ based in Britain. It will demonstrate how the South African apartheid regime operated through an ideologically aligned far right proxy to physically disrupt anti-apartheid meetings and to monitor exiled dissidents, their activities and potential sources of finance, as well as exploring how Chesterton helped to refine van den Bergh's personal intellectual framework and his definition of the who and what stood behind ‘sabotage’ and ‘subversion’ in South Africa.