This chapter provides an in-depth discussion of A.K. Chesterton’s role in disseminating anti-Semitic conspiracy theories to the extreme right after 1945. Drawing on Chesterton’s prolific and widely distributed output as an author and journalist, it argues that conspiratorial anti-Semitism provided an overarching rationale for the extreme right’s hostility towards non-white migrants, European integration and decolonization. In addition, it notes the extent to which Chesterton’s work facilitated international cooperation between neo-fascist and white nationalist groups outside of Britain, as well as the growth of ‘historical revisionism’ and Holocaust denial. This chapter concludes by briefly discussing the extent to which Chesterton’s conspiratorial ideology directly influenced John Tyndall, a leading figure in the National Front and the founder of the contemporary British National Party.