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UK–EU future relationship: defence and security co-operation

The UK is arguably the EU’s strongest defence power. But how will Brexit affect UK–EU defence and security arrangements?

UK and EU flag, Brexit


Will Brexit impact defence and security arrangements between the UK and the EU?

The EU does not have exclusive law-making powers in the area of defence but member states do work together on a number of defence-related issues, including research on defence technologies and joint military deployments. The UK’s involvement in these programmes will be affected by its decision to leave the EU.

NATO remains the overarching structure for European (and wider) defence co-operation. The UK also has important bilateral arrangements with individual member states, including France and Poland.

How will the UK and EU co-operate on defence and security during the transition period?

The UK participates in EU security and defence initiatives through the Common Security and Defence Policy (CSDP). The CSDP – previously known as the European Security and Defence Policy – was set up to allow EU member states to combine their security and defence efforts should the need arise. It followed the St Malo Summit of 1998 between France and the UK in response to the perceived failure of the EU to address the challenges of the Balkan Wars.

Under the CSDP, member states pool funding and resources to achieve agreed common goals, including:

  • humanitarian and rescue missions
  • conflict prevention and peacekeeping
  • joint disarmament operations
  • military advice and assistance
  • crisis management
  • post-conflict stabilisation.

The European Defence Agency plays an important role within the CSDP. It co-ordinates defence planning and assists EU member state governments with research and development.

The majority of the initiatives carried out through the CSDP are civilian, as opposed to military missions, meaning they use non-military personnel and/or tools.

EU missions have included:

  • European Union Force Althea, supporting the implementation of the Dayton Agreement in Bosnia Herzegovina
  • European Union Naval Force Atalanta, to combat piracy off the Horn of Africa
  • Operation Sophia, which identified and disposed of vessels used for people trafficking in the Mediterranean.

Involvement is not mandatory. Member states choose which operations they wish to be involved in, and national troops cannot be deployed without the member state’s agreement.

What other structures exist to support EU security co-operation?

Since the UK voted to leave the EU in 2016, other EU member states and EU institutions have taken steps to strengthen their military co-operation, including:

  • A European Defence Fund, which will fund research and development to support European defence companies.
  • The Coordinated Annual Review on Defence (CARD), which the EU says will "deepen defence cooperation and…coherence of spending plans".  

The EU has also established Permanent Structured Cooperation (PESCO), which aims to "to jointly develop defence capabilities and make them available for EU military operations". The UK, along with Denmark and Malta, chose not to participate in PESCO. 

The EU also co-operates on wider security matters, including policing and criminal justice. It is building a global satellite navigation system, known as Galileo, which provides services to individuals, businesses and public bodies, including on a secure platform used by policing and military authorities. The UK has contributed funding and expertise to the Galileo systems, and hosts key Galileo infrastructure on its south Atlantic territories.

How does the UK’s defence capability compare to the rest of the EU?

The UK is arguably the EU’s strongest defence power. It is one of only two member states possessing ‘full-spectrum’ military capabilities (including a nuclear deterrent), and is one of only six member states meeting the NATO target of spending 2% of gross domestic product on defence.

The UK also holds a permanent seat on the UN Security Council and has the largest military budget within the EU.

Will the UK have more control over its defence and security policy after Brexit?

The power to develop and implement security and defence policy lies with member states, not the EU.

When decisions are made at EU level – on whether or not to deploy troops, for example – they require unanimity among member state representatives. Any member state can veto a decision. Brexit will not change that in any way.

What do the UK and EU want security co-operation to look like after Brexit?

The October 2019 Political Declaration accompanying the Withdrawal Agreement expresses the intention of the UK and the EU to “support ambitious, close and lasting cooperation on external threats”. However, any future co-operation should respect both sides’ “strategic and security interests, and their respective legal orders”.

The EU’s mandate for negotiations on the future relationship with the UK adds that the UK and EU should explore new dialogues on foreign policy and be prepared to share information, including on sanctions – these dialogues could be set up before the end of the transition period. The UK could participate in EU defence missions and projects on a case-by-case basis, though any participation in EU projects and programmes must accept oversight from the European Court of Justice for matters of EU law.

The UK’s ministerial statement outlining the UK’s negotiation objectives for talks with the EU said the UK would be open to participation in EU programmes and instruments on a case-by-case basis.

How might this continued co-operation work?

Twenty-five non-EU states have already participated in CSDP operations. The CSDP also operates more formal ‘framework participation agreements’ with a number of non-EU countries, including Norway, Iceland and the US.

However, the government would prefer this co-operation to be based on “a combination of formal agreements enabling coordination on a case-by-case basis”, rather than one single formal treaty. This would be underpinned by regular consultation and co-ordination across all aspects of the UK–EU foreign policy relationship.

What will be the impact on the UK if existing arrangements are not maintained?

If the UK ceases to co-operate through CSDP mechanisms, there are other ways in which it can contribute to and influence security and defence measures in Europe and beyond. These include NATO, the Organization for Security and Co-operation in Europe, and bilateral agreements with member states. Brexit will not directly affect the UK’s membership of or role in NATO, which the government has said “will remain the cornerstone of European defence and security".

Several experts have argued that Brexit would not reduce the UK’s military power or position. The former head of the British army, General Sir Mike Jackson, says that the impact from departing the EU “is more of a policing and judicial matter rather than a military matter. The [UK’s] military dimension is provided by NATO”.

The House of Commons Library argues that existing research suggests that “the impact of Brexit on the UK’s military is arguably minimal in the near term. In the longer term, however, the UK’s ability to “influence or shape the CSDP agenda going forward will be significantly curtailed”.

The bigger impact will be on the UK’s defence industry: outside of the single market, UK companies will find it much harder to participate in European defence projects, and to access European funds.  

Where does Galileo fit in?

The EU could exclude the UK from other projects with a security dimension. However, the EU's draft mandate for negotiations on the future relationship suggests the UK could access the EU’s Galileo space programme – but only if the UK granted the EU access to its own navigation satellite system in return.

In December 2018, the government announced that the UK would be building its own Global Navigation Satellite System, although the ministerial statement on the UK’s negotiating objectives said the government would be open to exploring space co-operation with the EU.

Institute for Government

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