After 2016, UK governments have attempted to nurture bilateral relationships with EU27 member states in security and defence policy, areas not covered by the 2020 UK-EU trade deal. This article first provides an overview of the UK’s security bilateralism with EU27 countries in a strictly European context (i.e. outside the NATO framework). The analysis covers agreements with 18 EU countries concluded between 2016-22 to map the diversity of the UK’s approach to reinvigorating bilateralism in security and defence policy. To make sense of the UK’s bilateral strategy, the article questions whether the conclusion of so many agreements is a way to compensate for the absence of a separate EU-UK security treaty or a means to build leverage to secure UK interests. A comparison of the scope and content of the new bilateralism with that of security partnership proposed by Theresa May shows that, even under Boris Johnson, the aim appears to be to fill gaps in consultation, coordination, and capability-building. Finally, drawing on regime theory, the article demonstrates the challenges of replacing multilateralism with bilateralism. Whereas bilateralism enhances flexibility, this comes at the cost of leaving multiple gaps in terms of policy goals EU countries do not want to pursue bilaterally or because implementation is not legally binding. Nevertheless, this approach does leave space for a multilateral initiative such as the European Political Community.