Post-Brexit relationship
The post-Brexit relationship embodied in the TCA contains limited provisions on internal security, cyber and law‑enforcement cooperation. One of the key Brexit implications is the omission of a comprehensive EU–UK defence pact that some EU states have between themselves.
With Brexit, as of 1 January 2021, the CFSP and CSDP provisions no longer applied to the UK. The UK shifted from being an internal agenda‑setter within the EU to an external partner. As a result, the UK has no say, and no veto, over how EU defence progresses. Moreover, there is no official framework through which the UK and EU could develop and coordinate joint responses to emerging threats.
The major post-Brexit threats to the UK and the EU have been Russia’s invasion of Ukraine and changes in US policy. In response, EU defence and security have become more integrated, more focused on Russia and hybrid threats, and more industrially driven. By contrast, EU–UK cooperation relies on looser, ad hoc arrangements rather than a single overarching framework.
UK-EU cooperation is now based on specific agreements and projects rather than EU membership. These have developed in several ways. Examples include the 2024 German-British Trinity House agreements, the Joint Expeditionary Force (JEF) and the European Group of Five (the ‘E5’) which began in November 2024, as well as Franco-British efforts to support Ukraine.
- The E5 is a meeting of the defence ministers of Europe’s five biggest defence spenders and largest military powers: France, Germany, Italy, Poland and UK. John Healey is the UK’s current defence minister. At its seventh meeting on 20 February 2026 in Krakow, the E5 announced the ‘Low-Cost Effectors an Autonomous Platforms’ initiative (LEAP). LEAP will see the development of advanced low-cost air defence systems – such as autonomous drones or missiles – the first project of which will be delivered by 2027.
- JEF was founded in 2014 at a NATO summit and is made up of northern European nations with the UK leading it. The coalition involves Denmark, Finland, Estonia, Iceland, Latvia, Lithuania, the Netherlands, Sweden and Norway. JEF complements the NATO framework by being able to act with greater agility and speed.
At the May 2025 UK–EU summit both sides formalised a Security and Defence Partnership (SDP). The agreement provides for regular cooperation across different levels of government and different areas of security, including maritime, space, cyber and hybrid.
Do not confuse the E5 with the E6. Founded in January 2026, the E6 (France, Germany, Italy, the Netherlands, Poland, Spain) brings together the six major economies of the EU to focus on Europe’s resilience and long-term competitiveness.
EU defence developments
The EU’s Strategic Compass, adopted in March 2022, is a comprehensive action plan to strengthen the EU’s security and defence posture by 2030. In response to a rapidly deteriorating global security environment, it provides a shared threat assessment, a common strategic vision, and a detailed implementation roadmap for enhancing the EU’s ability to act, protect itself, invest in defence, and build global partnerships.
The success of the Strategic Compass depends on implementation by the member states. The EU’s progress since adoption includes:
- rapid operationalisation of the EU Rapid Deployment Capacity (RDC), force of up to 5,000 troops operational by 2025
- extensive military support and training for Ukraine, including tens of thousands of trained soldiers and multi‑billion‑euro assistance.
- new defence‑readiness initiatives such as Readiness 2030, an EU-wide plan to mobilise up to €800 billion for defence over the next several years, including the Security Action for Europe (SAFE) instrument, plus steps toward a strengthened EU defence industry.
The EU’s Permanent Structured Cooperation (PESCO) has deepened, with around 75 collaborative projects spanning land, maritime, air, cyber, space and joint enablers, and with stronger binding commitments on spending, interoperability and capability development. The EU has also opened PESCO to select third states (e.g. Canada, Norway, the US) for military mobility, signalling a more outward‑facing EU defence posture and tighter EU–NATO coordination.
The Coordinated Annual Review on Defence and the European Defence Fund is now tied more closely to PESCO. This means that capability planning, joint R&D and industrial policy are increasingly coordinated within the EU, rather than being left to national efforts.
UK participation in the PESCO military mobility project was under threat, because Spain had blocked the UK due to the ongoing dispute over border arrangements in Gibraltar. However, agreement on Gibraltar was reached in June 2025.
The European Defence Fund and other EU funding instruments have become more important as a way to compensate for fragmented national budgets and to address gaps amplified by the pandemic and Russia’s war. However, the EU has so far excluded the UK, unlike Canada, from participating fully in SAFE.
In addition, the EU has placed more emphasis on strengthening the European defence industrial base, ensuring supply‑chain security, and co‑developing “next generation” capabilities, rather than relying primarily on non‑EU suppliers.
Cybersecurity, hybrid threats, and protection of critical infrastructure (including underwater infrastructure) have become core themes in EU security workstreams.
Security and law‑enforcement
On internal security, the EU has continued to develop its databases, Prüm rules for DNA and fingerprint exchange, and frameworks for combatting terrorism, organised crime and foreign information manipulation.
Brexit meant the UK lost automatic access to some EU tools (notably the Schengen Information System), and cooperation now rests on the Trade and Cooperation Agreement (TCA) plus bilateral and mini‑lateral arrangements. Experts see these as workable but less seamless and more vulnerable to legal divergence over time.
Conclusion
While the UK remains one of Europe’s strongest military powers, its ability to collaborate with its allies is constrained. A more hostile security environment, coupled with Brexit, has also stimulated the EU to accelerate its own defence integration to compensate for losing a major military contributor.
In practice, UK-EU cooperation has concentrated on: support for Ukraine, participation in specific EU defence initiatives such as PESCO military mobility, information‑sharing agreements, cyber security and work on countering disinformation.
However, the UK’s exit from the Customs Union and the Single Market makes collaboration difficult at the manufacturing and company levels. Similarly, the EU’s focus on building its own industrial capability signals lost opportunities for the UK.
The UK and the EU face challenges in translating the ambitions of the Security and Defence Partnersip into tangible actions.