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The Consequences of Brexit for European Defence and Security

Sarah Lain and Veerle Nouwens
Occasional Papers, 11 April 2017
International Security Studies
This paper examines the contribution the UK currently makes to EU security in justice and home affairs, as well as through the Common Security and Defence Policy. It examines what the EU – and the UK – might lose if Brexit negotiations result in Britain withdrawing from participation in EU security structures.

In the wake of the triggering of Article 50 of the Lisbon Treaty, which formally began the UK’s exit process from the EU, this paper will examine some of the ways that the UK contributes to EU security in justice and home affairs, especially in relation to counterterrorism, and through the Common Security and Defence Policy (CSDP). In terms of justice and home affairs, the paper will focus specifically on the EU’s current intelligence and information-sharing platforms, especially those involved in counterterrorism. On the CSDP, it will look at the EU’s defence agencies and CSDP missions and operations. The objective is to understand some of the ways the UK contributes in these areas and what the UK might potentially lose post-Brexit, as well as what the EU might lose, if negotiations result in the UK withdrawing from participation in EU security structures. The paper will also identify some areas of mutual interest where continued cooperation between the UK and the EU post-Brexit may be desirable.

This paper is not intended to be an exhaustive survey of the many ways in which the UK contributes to EU security structures or the benefits it gains from involvement in these structures. As such, it does not examine the UK’s role in issues such as anti-money laundering or criminal asset freezing, nor does it discuss the UK’s role in platforms such as Eurojust or the European Anti-Fraud Office (L’office européen de lutte antifraude, or OLAF). Rather, it looks only at some of the contributions that the UK makes, focusing in particular on counterterrorism.

The paper is based on a review of the existing academic literature, government and EU policy documents and legislation, and information from law enforcement. It stemmed from a December 2016 workshop jointly organised by RUSI and the Friedrich-Ebert-Stiftung (FES). The objective was to discuss the consequences of Brexit for European security and defence. During the workshop, parliamentarians and experts from the UK and Germany shared their views and insights on what the EU and the UK might lose with a British departure from CSDP and joint institutions such as Europol.

NOTE: This paper, originally published in April 2017, was updated in August 2017. 

Sarah Lain
Associate Fellow

Sarah Lain is currently a Research Advisor, based in Kyiv. She previously served as a Research Fellow at RUSI in the International... read more

Veerle Nouwens
Research Fellow

Veerle Nouwens is a Research Fellow at the International Security Studies Department of the Royal United Services Institute, focusing on... read more

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