This paper aims to study how an event, happening within a political community characterised by a high level of interdependence, has an impact on the defence policy of its members. To do so, the paper focuses on British-Polish defence relations after Brexit. Indeed, the United Kingdom signed a defence cooperation agreement (dca) with Poland in 2017, which is the second with an EU/nato Member State (MS) after the Lancaster House treaty signed with France. This case-study questions the thesis positing that dcas are unlikely to happen between EU/nato MS as it would lead to overlaps and decoupling. It also determines to what extent this treaty is part of a British strategy to re-create a security network in Europe after Brexit to deter Russia, which is considered as one of the main threats for both countries. Finally, this study deals with the political uses of history. The research analyses how British and Polish actors select memory mines to consolidate friendship in time of uncertainty but also as a shaming strategy.