The UK-EU security relationship has become increasingly important amid uncertainties about US reliability, argues Max Becker, Johanna Flach and Dr. Nicolai von Ondarza. In this article they explore pathways to strengthen defence cooperation.
At a time when the reliability of the US as an ally is under question and Europeans have to take a much greater, if not full, responsibility for their own security, the UK-EU security relationship has suddenly taken on a new importance. Now is the time to explore practical pathways for a deeper UK engagement with different EU defence instruments. While the political will for closer cooperation is publicly stated on both sides, the path forward is riddled with legal, political, and strategic challenges that require careful navigation.
The EU’s defence architecture is multifaceted, encompassing an array of instruments which often allow for third country participation, with countries like NATO-ally Norway participating in quite a few EU defence initiatives. But as the Johnson government decided to exclude any structural cooperation with the EU in these areas, EU-UK cooperation has been limited to a Security of Information Agreement and ad-hoc cooperation in the wake of the Russian invasion of Ukraine.
The EU’s third country rules in Common Security and Defence Policy (CSDP)
To better understand the options for UK-EU cooperation on defence, we assessed to what extent current EU third country rules allow for UK participation and how these rules relate to the UK’s red lines on cooperation with the Union:
Permanent Structured Cooperation (PESCO) is an instrument that allows groups of EU member states to cooperate on military capabilities, and allows for third-state participation on a project-by-project basis. However, the EU wants to avoid dependencies on any third country and wants to maintain the final decision-making capacity. That means only a few projects are open to the participation of third countries, and these do not involve the development of skills or technologies. The most prominent project among third countries is Military Mobility. Whilst the United Kingdom was invited in 2022, it has not yet become a full member due to difficulties over Gibraltar.
The European Defence Agency (EDA) adds another layer of complexity. While third countries like Norway and the US have framework agreements allowing for selective participation, these agreements come without decision-making rights. CSDP missions and operations, which have seen UK involvement in the past, also pose challenges: both individual agreements and Framework Participation Agreements allow only a limited influence in mission planning and execution. This does not violate regular UK red lines, but would reduce the potential for a leadership role the UK has usually claimed in CSDP operations with considerable British participation.
Deeper defence industrial cooperation is with few exceptions only open to EU or associated countries, meaning those in the European Economic Area such as Norway. Designed to strengthen EU defence R&D, the European Defence Fund (EDF) only allows for UK companies to participate if they waive EU funding and comply with strict intellectual property rights (IPR) rules. Part of these restrictions even apply to EU-based companies under UK ownership. Any technology or products developed under the EDF must remain under EU control, leaving concerns about the UK’s ability to retain ownership or commercialise innovation. In addition, compliance with dual-use regulations and export controls further complicate the UK’s involvement, as components or technologies may face restrictions if transferred across borders.
The European Defence Industry Reinforcement through Common Procurement Act (EDIRPA) and the Act in Support of Ammunition Production (ASAP) focus on joint procurement and scaling ammunition production. UK firms currently do not participate. To do so they would need to comply with EU procurement rules and navigate complex IPR agreements as well as export controls and licensing for sensitive technologies.
A four-stage model towards a special partnership
This web of restrictive third country rules shows that expectation management is needed. The UK has chosen to be outside the single market, and the EU has largely locked out third countries outside its market. At present, there is no easy way to fully participate in EU defence initiatives. Based on existing EU rules and the UK’s red lines, we have developed a four-stage model on what this relationship could look like.
The first stage describes very limited engagement, as the UK had in 2020-22, cooperating primarily with individual EU member states on a bilateral, multilateral, or NATO level, without formal defence coordination. The second stage, where the UK currently stands, can be characterised as ad-hoc partnership. This includes limited coordination through instruments like the Security of Information Agreement and selective cooperation on CSDP instruments, such as PESCO´s military mobility.
Illustration 1 – Four stages of third country security and defence cooperation with the EU
The third level is a structured partnership with full coordination and broader cooperation. This includes a wider range of PESCO projects in which the UK would participate, an administrative agreement with the EDA allowing for participation in EDA projects, as well as a Framework Agreement for participation in CSDP missions and operations. This would be possible under current UK red lines, and could form the basis for the EU-UK security pact envisioned by Labour.
The fourth stage would be a special partnership in security and defence. Due to the linkages made by the EU between defence industrial cooperation and the single market, this would require either reintegration into the EU’s single market, a revision of the rules on third countries, or the creation of a special status for the UK. In the current geopolitical changes, the two latter options have become more likely.
The strategic imperative for closer UK-EU defence ties is clear. Shared security threats – from Russian aggression in Ukraine to evolving hybrid threats and the questions of reliability with regard to the US – demand coordinated responses. But as our analysis shows good intentions, as recently declared by Kaja Kallas and David Lammy, are not enough. Rather than holding on to red lines on both sides, it is time for both the EU and the UK to step up. For the EU, this should entail significantly adapting the third country rules to allow for UK participation in defence industrial projects, even if it will likely not rejoin the single market. For the UK, this will entail accepting that for the defence and defence industrial cooperation organised in the EU, even full participation rights will not come with full decision-making rights. Finding a right balance on this should be imperative as Europe arms up.
By Max Becker,Johanna Flach, Research Assistant and Student Assistant in the EU/Europe Research Division at SWP, and Dr. Nicolai von Ondarza, Head of the EU/Europe Research Division at SWP and an Associate Fellow at Chatham House.
This article draws on the analysis presented in the working paper “Third-State Participation in CSDP: Options for the UK” by Max Becker, Johanna Flach, and Nicolai von Ondarza, published by the German Institute for International and Security Affairs (SWP).