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Relations between Britain and the European Union have experienced significant fluctuations since the post-Brexit era. These ties grew more complex with the onset of the war in Ukraine and Russia. This complexity was further compounded, and the mutual dependency of both sides laid bare, by Trump's rise to power in the United States and the sweeping changes to that country's national defense doctrine. Britain's position as a geostrategic power is of immense importance to Europe, while the Union, as an economic power, can largely cover London's shortfalls. Thus, it appears both powers have reached a mutual understanding: they need each other for survival and to navigate the challenges of the new international order.
When Brussels and London reached a point where necessary cooperation, particularly in security, was imperative, they signed a security pact known as the Strategic Partnership Agreement. This treaty represents a strategic shift in Europe's security architecture. After the war in Ukraine and warnings from the United States, Europe found itself in a state of strategic loneliness and military weakness. To overcome the crisis, it turned to strategic cooperation with Britain. London had clearly demonstrated Europe's importance to itself through extensive support for Ukraine, supplying and training its army, playing a crucial role in its war resistance. Furthermore, Britain, alongside France, is one of the only European countries possessing a full-spectrum nuclear defense and operational umbrella—a critical factor for European security in the face of a potential nuclear threat from Russia. This drove Europe toward a security and military pact with Britain, designed to address both the Union's needs and London's concerns.
The institutional design of the EU-UK security and defense partnership reflects a conscious emphasis on flexibility and political discretion for both sides. Unlike binding defense treaties or supranational security arrangements, this partnership is designed as a flexible, non-binding framework enabling targeted cooperation in specific areas such as cyber defense, crisis management, military mobility, and countering hybrid threats. Importantly, this agreement does not grant Britain permanent participation in key EU defense institutions like the European Defense Agency (EDA) or the Permanent Structured Cooperation (PESCO). Britain's access to specific EU projects is determined through case-by-case, dedicated negotiations. This ad-hoc approach allows both parties to cooperate where their interests align without committing to institutional and binding frameworks that would limit their strategic flexibility. Consequently, the overall architecture of this partnership reflects a logic grounded in preserving sovereignty, managing relative interests, and avoiding ambiguity in binding collective security commitments. This very feature is a factor in the treaty's agility and efficiency, enabling it to accelerate cooperation and create as few barriers as possible.
It must be considered that one of the main obstacles to deepening defense convergence between Britain and the EU is the difference in their defense industrial and regulatory frameworks. In recent years, the EU has focused on integrating its internal defense market through mechanisms like the European Defence Fund (EDF) and the European Defence Industrial Programme (EDIP). These approaches are specifically designed to encourage joint development and procurement among member states, reduce dependency on non-member suppliers, and strengthen the European Defence Technological and Industrial Base (EDTIB). These developments pose simultaneous strategic and economic challenges for Britain.
After years of underinvestment and industrial downsizing, The UK defense industry faces numerous structural deficiencies—from a shortage of skilled personnel and weak supply chains to limited production capacity in military industrial centers. These problems have been exacerbated by post-Brexit trade frictions and long-term budgetary pressures. Therefore, Britain's selective participation in EU defense programs stems less from a desire for reintegration and more from a material and financial necessity to access mechanisms for joint procurement, advanced technologies, and shared research and development. This partnership is a tool to compensate for London's internal shortcomings, without altering Britain's fundamental preference for maintaining strategic independence.
At the strategic level, London is compelled to balance its special relationship with Washington and its ties with Brussels. The historical dependency on the United States remains a valuable asset, but it also carries risks for London should future American administrations disengage from Europe. Conversely, closer security cooperation with the EU provides Britain with greater strategic depth and resilience. Perhaps the only sustainable path for a post-Brexit Britain that wishes to remain a pillar of European security is not choosing between America and Europe, but finding a way to align and shape a balance between both its allied powers.
Ultimately, it must be said that despite expanding cooperation in some areas, Britain and the European Union remain committed to different strategic paths. Britain defines itself as a global security actor within the international system, viewing the continuation of a central role in NATO, strategic reliance on the United States, and a network of bilateral defense agreements as the main pillars of its security policy.
In contrast, the EU has placed the concept of "strategic autonomy" at the heart of its security strategy—a concept aimed at reducing dependency on extra-regional actors and strengthening an independent European defense capacity. This identity distinction is clearly reflected in the text and legal framework of the Strategic Partnership Agreement, where cooperation is explicitly conditioned on respecting each party's institutional and legal frameworks. This indicates both sides' high sensitivity to the issue of sovereignty and their aversion to binding institutional commitments. In practice, cooperation between Britain and the EU reflects a new perspective on topic-based, non-hierarchical alliances—frameworks that enable selective coordination without surrendering strategic control. This model allows both sides to cooperate in shared security domains without submitting to binding institutional obligations. In such a context, the London-Brussels partnership is predominantly pragmatic in nature, aimed at managing shared vulnerabilities based on realist necessity, not moving toward comprehensive integration.
Translated by Ashraf Hemmati from the original Persian article written by Amin Mahdavi
[1] https://blogs.surrey.ac.uk/centre-britain-and-europe/2025/09/15/britains-return-londons-role-in-shaping-europes-defence-future
[1] https://www.chathamhouse.org/2022/02/uk-must-not-dismiss-european-strategic-autonomy
[1] https://www.geopoliticalmonitor.com/uk-eu-defense-pact-strategic-shift-or-stopgap-fix
[1]https://blogs.surrey.ac.uk/centre-britain-and-europe/2025/09/15/britains-return-londons-role-in-shaping-europes-defence-future
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