11. Defence and security

Section contents


Brexit implications for defence and security include:

  • Security threats (such as terrorism and cyber-crime) facing UK and EU27 require cross-border cooperation
  • Brexit makes it difficult for UK to influence EU27 policy for defence and security effectively
  • UK now has no decision-making rights, and no veto, over EU defence and security policy
  • Defence
    • Foreign and defence policy cooperation does not form part of the EU-UK Trade and Cooperation Agreement
    • UK regards NATO as cornerstone for EU defence
    • UK has no formal post-Brexit arrangements in place for dialogue
  • Security
    • UK’s security continues to depends on extensive intelligence sharing with EU27
    • Under the TCA:
      • EU and UK will continue to share DNA and fingerprint data through Prüm, and to transfer Passenger Name Record data.
      • UK has lost access to EU databases – notably SIS
      • UK will cooperate with Europol and Eurojust, including data-sharing.

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Defence and security threats

The major threats currently facing the UK (and the EU27) are cross-border and transnational:

  • Terrorism
  • Global migration crisis (partly linked to climate change) and regional rivalries
  • Security situation in the Middle East (e.g. Syria, Libya) and ungoverned spaces
  • Unpredictability of the Trump administration
  • Eastern Europe tensions and Ukraine conflict  – increasing Russian assertiveness and incursions into EU air and naval space
  • Cross-border crime
  • Cyber security
  • Foreign interference in elections.

Given the cross-border nature of these threats, addressing them requires international collaboration, cooperation and responses.

Source: European Commission, White Paper on Defence, June 2017



EU defence

The Lisbon Treaty, which came into force in 2009, strengthens the solidarity between EU countries in dealing with external threats by introducing a mutual defence clause (in Article  42(7) of the Treaty on European Union). This clause provides that if an EU country is the victim of armed aggression on its territory, the other EU countries have an obligation to aid and assist it by all the means in their power.

Common Security and Defence Policy (CSDP)

The Common Security and Defence Policy (CSDP) is a major element of the Common Foreign and Security Policy of the EU and is the domain of EU policy covering defence and military aspects. The CSDP provides the framework for military operations and civilian missions conducted in support of the overarching EU Common Foreign and Security Policy. The UK, along with France, has been a prime mover in its development. The CSDP maintains clear “red lines”, such as the non-duplication of NATO’s operational planning and command structures.

The UK has played a leading role in CSDP activities but, long before the referendum, had started to walk away from the CSDP and cut back its contribution to EU deployments. It now ranks only fifth among the contributors to CSDP military operations, after France, Italy, Germany and Spain. The UK ranks seventh for civilian missions, after Germany, Netherlands, Poland, Sweden, France and Finland.

Synchronised Armed Forces Europe (SAFE) was founded in 2009 and is a concept for ever closer synchronisation of the European forces under the Common Security and Defence Policy. Participation in SAFE is voluntary.

Permanent Structured Cooperation (PESCO)

Article 42 also provides for permanent structured cooperation between the armed forces of a subset of member states. The treaty set out the means for this in Permanent Structured Cooperation (PESCO). Through inter-governmental cooperation, PESCO allows member states to jointly develop military capabilities, invest in shared projects and enhance their respective armed forces.

In late 2017, the European Council (the EU heads of state) committed to deeper defence cooperation under PESCO involving 25 member states (excluding Malta, Denmark and the UK). This comprises 17 joint defence projects to begin in 2018, including establishing a pan-European military training centre, improving capability development and introducing common standards for military radio communication. Decision-making remains with individual member states but the programme provides operational steps towards a longer-term Defence Union. On defence matters, unanimity is required so, for example, each member state has the ability to veto a European Army.


The UK has regarded NATO as the cornerstone foe defence, with the EU playing a subsidiary and complementary role.

Figure 11.1 shows the relationship between EU and NATO membership.

  • Austria, Finland, Ireland, Malta and Sweden are in the EU, but not in NATO. They are members of  NATO’s Partnership for Peace (PfP) programme and participate in NATO meetings.
  • Albania, Canada, Iceland, Norway, Turkey and the United States, which are members of NATO but not members of the EU, participate in all NATO-EU meetings.

On a national basis, the UK has the second largest defence budget in NATO, after the US.

The EU has the third largest arsenal of nuclear weapons, after the United States (6,800 including those deployed in EU) and Russia (7,000). The EU possesses 525 warheads, and hosts between 90 and 130 US warheads. Six EU states host nuclear weapons:

  • France (300 warheads) and UK (215) have their own;
  • Belgium, Germany, Italy and the Netherlands host US nuclear weapons as part of NATO’s nuclear sharing policy (90-130).
Sources: Federation of American Scientists, Status of World Nuclear Forces
House of Commons Library, European defence: where is it heading?, briefing paper 8216, 30 January 2018


Global trends in defence spending

While most defence budgets in Europe have been contracting (military expenditure among EU28 had fallen by 9% between 2005 and 2014), countries such as China, Russia and Saudi Arabia have been upgrading their armies on an unprecedented scale.  Figures 11.2 shows global trends in defence spending and illustrates how overall EU defence spending has declined relative to others.

The US already invests more than twice as much on defence than all member states combined and increased its budget by almost 10% in 2018. China has increased its budget by 150% over the past decade, with a further rise of 7% expected in 2017, while Russia invested 5.4% of its GDP on defence in 2016.

Collectively, the EU is the world’s second largest military spender. However the EU is far from being the second largest military power. This is partly due to inefficiency in spending and a lack of interoperability.


Source:  European Commission, EPSC, In Defence of Europe, Defence Integration as a Response to Europe’s Strategic Moment
US defence spending

In 2017, US defence spending was more than the next top ten countries combined. The UK was the fifth spender globally and the top spender in the EU. See Figure 11.3.

Source: International Institute for Strategic Studies



EU defence spending

Over the last two decades, EU defence spending has declined relative to others, but has been increasing recently. See Figure 11.4.


The EU spends about 1.4% of GDP on defence. The UK and France are the two members that spend the most on defence relative to GDP (the UK at around 2%, France at around 1.8% GDP – see Figure 11.5). They also spend the most in absolute terms ($51 billion and $49 billion respectively in 2017- see Figure 11.3).

Source: Eurostat


European collaboration on defence spending

There is a long history of collaboration between member states on defence (see figure 11.6). Collaboration is currently being reinforced through PESCO (discussed above).

Source: European Commission position paper – EPSC Strategic Notes Issue 4 June 2015


However, European countries continue to pursue costly duplications of military capabilities. In 2013, 84% of all equipment procurement took place at national level, thereby depriving countries of the cost savings that come with scale. See Figure 11.7

The lack of interoperability between 28 European armies significantly slows down the EU’s ability to intervene collectively in expeditionary missions where European interests and values are at stake.

Decreases in spending result in reduced investment in new technologies and prevent renewal of military programmes.

Source: European Commission position paper – EPSC Strategic Notes Issue 4 June 2015



Brexit implications for defence

Political Declaration and TCA

In its 2017 partnership paper on foreign policy, defence and development , the British Government recognised that continued close cooperation is vital for both UK and EU27 interests. The paper set out the UK’s aspirations but did not make any firm proposals on how future cooperation could be structured. The paper stated that the UK wanted a “deep and special partnership” that goes beyond any existing third party agreement with the EU. It concludes: “It is the UK’s ambition to work as closely as possible together with the EU, protecting our citizens, promoting our values and ensuring the future security of our continent.”

Formal foreign and defence policy cooperation does not form part of the EU-UK Trade and Cooperation Agreement (TCA). The Political Declaration of October 2019  included Foreign Policy and Defence Cooperation. However, at the request of the British Government, foreign policy and defence cooperation were not part of the 2020 negotiations. The Government prefers a flexible, ad-hoc approach to foreign policy and defence cooperation, “within a framework of broader friendly dialogue and cooperation between the UK and the EU”. 

As of 1 January 2021 CFSP and CSDP provisions no longer apply to the UK. The TCA refers to the two parties’ recognition of “the importance of global co-operation to address issues of shared interest”. The Common Provisions of the TCA also refer to a number of common principles with an international dimension, such as democracy, the rule of law, respect for human rights and the need for cooperation and coordination within multinational institutions.

Going forward the UK will have no say, and no veto, over how EU defence progresses. There is now no official framework in place through which the UK and EU can develop and coordinate joint responses to emerging foreign policy challenges. 


Future arrangements will need to mitigate the key risks of Brexit to the UK’s defence and security, which include:

  • Reduced UK-EU co-operation over policing and judicial affairs;
  • Weaker diplomatic collaboration;
  • Impeded intelligence-sharing;
  • Diverging defence and security policies; and
  • Damage to UK defence industry due to trade impacts.

Risks of Brexit to the EU27’s defence and security include:

  • An economically weak or politically fragmented UK would be a major security concern for both the EU (and the US).
  • Although many bilateral initiatives and arrangements between the UK and EU states (e.g. the Combined Joint Expeditionary Force) are unlikely to be directly affected by Brexit (since they exist outside of EU institutional structures), indirect effects (such as Brexit-induced economic decline or the diminution of British power and influence overseas) could damage these arrangements to the detriment of both parties.
Wider implications

Wider implications include:

  • Uncertainty regarding the likely institutional impacts of Brexit. There are questions over Britain’s future role, if any, in EU defence and security missions and initiatives as well as the ability of the EU to deliver military effect in the absence of UK military capabilities.
  • Proposals for a permanent EU military force have become more vocal in the last year, although there appears to have been little detailed work on what this might look like in practice.
  • Uncertainty extends to NATO with some questioning whether Brexit heralds a wider strategic retreat by the UK with impacts for NATO, and whether the Alliance will inevitably be weakened by the diversion of European defence resources into the creation of a standing EU military body.
Source: RAND Europe, A snapshot of international perspectives on the implications of the UK’s decision to leave the EU, 2017

With Brexit, the reality is that in the longer term, as a third party state outside of the EU, the UK will have no decision-making rights, and no veto, over how EU defence policy evolves. At the same time, the UK will not want to commit its considerable defence assets without a say over operations and other matters.

The issue of finding a way to participate in EU decision-making and policy formulation without formal voting rights is common across many policy areas affected by Brexit.  It is clearly in the UK’s interests to continue to have influence in EU27 defence policy and operations. It is also in the EU27’s interests to keep the UK as a close partner on defence and security. However, Brexit is likely to make it difficult to do so.


House of Commons, Research Briefing, End of Brexit transition: implications for defence and foreign policy cooperation, 19 January 2021



Current situation

EU-level security cooperation

As a member of the EU, the UK’s counter-terrorism and crime operations have depended on extensive formal and informal networks of intelligence and data sharing, including, at the EU level:

  1. Europol, the EU’s law enforcement agency, employing over 900 people, is generally considered invaluable both for intelligence sharing and at the operational level;
  2. Schengen Information System (SIS), which the UK is part of despite not being in the Schengen travel area.  Thousands of EU27 SIS-issued and UK-issued alerts are accessed by law enforcement and border agencies each year. (As the UK is outside Schengen, it already checks the security risk of all arrivals into the country, whether from the EU or not.);
  3. Passenger Name Record data (obliges airlines to hand over passenger records to EU Member States to prevent terrorism and serious crime, including trafficking in drugs, people or weapons, cybercrime, and sexual exploitation of children).
  4. European Criminal Records Information System (ECRIS);
  5. European Arrest Warrant (make extradition of criminal suspects simpler);
  6. Eurojust which was set-up to promote judicial cooperation in criminal matters;
  7. Frontex – the EU Border Agency and Coast Guard; and
  8. Prum Convention a treaty signed in 2005 between Belgium, Germany, Spain, France, Luxembourg, the Netherlands and Austria on cross-border cooperation, particularly in combating terrorism, cross-border crime and illegal migration. Some provisions were later subsumed into EU law and therefore adopted by the UK.
Other security cooperation

Other security arrangements include:

  • Le Touquet – trilateral agreement between the UK, Belgium and France, whereby the UK has its border checks in Calais for ferries (Paris and Brussels for Eurostar) while France has its in Dover and at St Pancras station.
  • UK-Irish border – the hard border has been discontinued. Visitors from outside the EU can visit both countries on a single visa. The virtual disappearance of the border contributes to continued peace in the north of Ireland.
UK aspirations

In September 2017, the UK government published a future partnership paper on security, law enforcement and criminal justice which described at length the strengths and capabilities of the EU28’s current arrangements and the UK’s significant contribution to them.  Moving on to Brexit, it noted that current third country arrangements would be sub-optimal for the UK and the EU27. The paper made no firm proposals for the future arrangements between the UK and the EU.

Theresa May reinforced the UK’s position in a speech to a Security Conference in Munich on 17 February 2018 where she urged the EU to accelerate a new EU-UK security partnership in 2018. Mrs May offered to carve out a special exemption on the remit of the ECJ to oversee Britain’s continued involvement in pan-European crime fighting agencies such as Europol and Eurojust, as well as the European Arrest Warrant.


Brexit impact on security

The EU-UK Trade and Cooperation Agreement covers security cooperation. There are supplementary joint declarations relating to PNR, surrender, the exchange of criminal record information and cooperation between law enforcement authorities. Both sides’ commitments to human rights underpin the agreement, including the European Convention on Human Rights, including a high level of protection for personal data.

The UK and the EU will:continue to share DNA and fingerprint data through Prüm, and to transfer Passenger Name Record (PNR) data. However, the UK has lost access to EU databases. Notably, the UK has lost access to SIS II which allows for real-time sharing of data on wanted or missing persons or objects. The UK police forces consulted the database 600 million times in 2019.

The EU and UK will be able to share information relevant to operations, including on wanted or missing persons and criminal record information. This will be in response to requests from the UK or EU member states and can be shared proactively.

There will be a new surrender agreement to replace of the European Arrest Warrant. There are clear provisions relating to:

  • How, and under what circumstances, the surrender must take place;
  • What grounds a request can be refused.

The agreement also includes;

  • Provisions to ensure mutual legal assistance, which includes a time limit for responding to any requests;
  • Obligations on both sides to combat money laundering and terrorist financing including sharing relevant information, or confiscating assets, when requested.

The agreement provides a framework for co-operation with Europol and Eurojust, including data-sharing. There will be supplementary agreements directly between the UK and each agency. The proposed relationship with Europol and Eurojust is similar to the EU’s surrender agreement with Norway and Iceland (although that agreement took ten years to negotiate). The UK will be able to:

  • Second liaison officers to Europol (and vice versa) who will be able to attend operational meetings.
  • Take part in operational analysis projects as well as attend the Europol Heads of Unit meetings as an observer.
  • Second a liaison prosecutor to Eurojust and Eurojust who will be able to post a liaison magistrate to the UK.
    • The liaison prosecutor will be able to attend strategic and operational meetings if invited.


Institute for Government, UK–EU future relationship: the deal, Law and justice, January 2021



Last updated on 11th May 2024 by Richard Barfield