Overseas diasporas have long been exploited by terrorist organisations seeking funding and support from areas beyond their operation. The Kurdistan Worker’s Party (PKK), active in south-eastern Turkey, is no exception and maintains a significant international presence. This paper uses 73 survey responses and 13 interviews amongst London’s Turkish and Kurdish diaspora to provide an original and comprehensive insight into the PKK’s overseas operations, including their offending patterns, methods, hotspots, offender/victim profiles and existing countermeasures. Respondents were also consulted on new community-based prevention measures designed to address limited law enforcement responses and the laissez-faire approaches of diaspora host countries. This strategy, which combines crime science and behavioural economic theories, consists of Clarke’s “Situational Crime Prevention” theory and Thaler and Sunstein’s “Nudge” theory (SCP+N). The results indicate that the PKK creates criminal opportunities by “legitimising” itself across diasporas by invoking ideological sympathy and social dependence (conceptualised as “constructed legitimisers”), ensuring minimal resistance to its activities. SCP+N is motivated as an effective counterstrategy, addressing both the rational and impulsive nature of offending. The overall theoretical contribution of this paper is to assess overseas terrorist financing through a prevention-oriented, situational and behavioural framework, and to propose a community-based strategy to effectively counter such activities.