EU–UK Relations: Missing the moment in European Security?

Why is it taking so long for the European Union and the United Kingdom to agree on a formal security and defence partnership?

This article was first published by the UCL as part of a series on perspectives from across UCL and beyond on the changing geopolitical order, and the implications for Europe, the European Union and the EU-UK relationship. Find more articles here.

Since the UK’s general election last summer, both the EU and UK have acknowledged the strategic importance of working together—particularly as Europe faces intensifying security challenges. The Labour Party’s ambition for a comprehensive ‘security pact’—encompassing not only defence but also cross-border intelligence, policing, and judicial cooperation—was signaled well in advance of its electoral victory. The new UK government moved swiftly to improve bilateral relations with EU member states, notably striking a new agreement on security and defence cooperation with Germany. 

Yet, setting aside the complexities inherent in negotiating such an expansive agreement, the lack of a formal EU–UK accord on foreign, security, and defence policy suggests that, despite the positive rhetoric, something remains amiss. The delay is increasingly difficult to justify, especially in light of Europe’s radically altered security landscape under a second Trump administration. 

President Trump’s ‘peace process’—designed to settle Russia’s war on Ukraine on terms favourable to the Putin regime—has conspicuously excluded European allies from negotiations with Moscow. This has fractured what had previously been a unified and closely coordinated transatlantic approach to diplomacy and military support for Kyiv. The breakdown in cooperation has triggered wider questioning of the United States’ role in Europe’s security and defence. 

In response, European governments—including the UK, and most dramatically, Germany’s incoming administration—have mobilised significant new financial resources for defence. The European Commission and the EU High Representative have also launched ambitious initiatives, including the ReArm Europe Plan/Readiness 2030. These programmes aim to reclassify member state defence expenditure, reallocate existing commitments towards defence procurement, and raise debt funding to accelerate Europe’s defence industrial capacity and procurement of new capabilities. 

These measures are designed to prepare Europe for the potential withdrawal of US military capabilities, which currently underpin NATO’s collective defence. A notable indicator of this shift in strategic thinking is the growing public debate—particularly in Germany and Poland—over whether Europe should hedge against a possible end to the US nuclear deterrent commitment on the continent. 

Moving Beyond Organised Ad Hocery 

Despite the absence of substantive provisions for foreign, security, and defence policy in the EU–UK Trade and Cooperation Agreement, cooperation between the two has evolved significantly since Russia’s full-scale invasion of Ukraine in February 2022. 

Both the EU and UK have played critical roles in supporting Ukraine’s defence and resilience. Their joint efforts have demonstrated the practical benefits of close cooperation, yet this collaboration has remained largely informal and reactive—a form of what might be termed ‘organised ad hocery’—rather than embedded within a structured and strategic partnership. 

Direct EU–UK cooperation on Ukraine takes place within a broader framework of coordination that includes the G7, NATO, the Ramstein process, longstanding minilateral arrangements such as the Joint Expeditionary Force, newer groupings like the E5 (France, Germany, Italy, Poland, and the UK), and extensive bilateral consultations. 

These overlapping structures have proved effective in ensuring the UK remains enmeshed in a complex but functional web of cooperation with the EU and its member states on European security. However, beyond their shared approach to Ukraine, EU–UK collaboration on wider international issues—ranging from China, climate change, and energy, to AI, the Middle East, and US efforts to undermine the multilateral trading order—remains fragmented. While their interests are not identical, they are sufficiently aligned to justify framing their relationship as an alliance. Thinking of it in these terms highlights why a formal agreement based on existing EU models sets ambitions for the relationship far too low. 

Rethinking the Framework for EU–UK Security Cooperation 

Adopting one of the EU’s existing foreign, security, and defence cooperation models for third countries is feasible but likely to add minimal value unless framed in different terms. Agreements granting the UK participation in the EU’s Common Security and Defence Policy (CSDP) operations would be largely performative, connecting the UK to activities that have become increasingly peripheral to the future of European military security. 

The real debate about Europe’s defence now centres on the future of NATO’s European pillar—and the extent to which the alliance could operate, or be repurposed, in the event of diminished or absent US participation. 

A more significant question for EU–UK security and defence relations concerns the UK’s potential participation in the defence industrial initiatives proposed by the European Commission and the EU High Representative in their recent Defence White Paper. Since Brexit, the evolution of EU defence industrial policy has left the UK outside the scope of its most integrated frameworks—unlike non-EU NATO member Norway, which benefits from European Economic Area (EEA) membership. 

An exception has (understandably) been made for Ukraine, granting it participation on terms similar to Norway’s. However, no equivalent offer has been extended to the UK. This omission undermines the messaging of both sides and calls into question their stated commitment to a renewed and deepened security and defence relationship. Extending the same terms to the UK would have sent an unequivocal signal that both London and Brussels are serious about future cooperation. 

The May summit: Coming too late? 

There is speculation that this issue will be addressed at the EU–UK summit in May, potentially through an agreement that alters the UK’s status within EU defence industrial arrangements. But if such a change is on the horizon, the current approach to signalling it is muddled. 

The summit may well mark a new phase of détente between London and Brussels, but the publicly demonstrated pace of progress remains worryingly slow, particularly given the urgency of the security challenges Europe now faces. The absence of a formal EU–UK security and defence partnership is an increasingly glaring omission in efforts to construct a coherent European response to the evolving security order. 

At a time when Europe must prepare for the potential loss of US guarantees, the EU and UK cannot afford to miss the moment.