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Research Questions

  1. What might be the defence and security implications of the UK leaving the EU for the UK, Europe, or globally?
  2. What steps could policymakers in the UK, Europe and globally take in the short term to address, mitigate or extract the most benefit from the implications of Brexit for defence and security?
  3. What research questions merit closest attention by defence and security policymakers and the research community in the context of deep uncertainty about Brexit?

This RAND study examines the potential defence and security implications of the United Kingdom's (UK) decision to leave the European Union ('Brexit'). Specifically, it seeks to identify those policy areas, strategic concerns or military capabilities that might be most affected, as well as to explore and define the spectrum of possible outcomes in each area. The goal is to help policymakers both inside and outside the UK to understand the key questions provoked by Brexit, and thus to inform how defence and security actors begin to plan for, mitigate and address these uncertainties as the UK begins negotiations to leave the European Union.

This RAND study comprises three publications:

  1. This compendium report, which provides the greatest level of detail on the analysis conducted.
  2. The associated overview report, which outlines the principal findings of the study.
  3. A standalone international perspectives report, which provides a snapshot of selected international perspectives on Brexit following the June 2016 referendum.

Key Findings

International cooperation

  • Defence may be less immediately affected by Brexit than areas such as labour policy or trade. Much international defence cooperation takes place through NATO or bilaterally — as will remain the case after the UK leaves the EU.
  • Analysis highlights the need for sustainable post-Brexit solutions for defence and security. This will require effective compromise and continued engagement between the UK and EU, which have both benefited from information-sharing, the joint work of bodies like Europol, and use of the European Arrest Warrant.

Strategic ambitions

  • Nonetheless, Brexit will require that both the UK and EU re-evaluate their strategic goals, what role they want to play in the world, and whether they have the capabilities and collaborative frameworks needed to achieve them.

Future of EU defence and security

  • The loss of the UK is a significant loss for the EU on defence. Some estimate that Brexit could reduce the EU's defence capabilities by a quarter. EU leaders are now working on plans to promote more EU defence integration, perhaps through a European operational headquarters — a plan long blocked by the UK while an EU member.

Regional implications

  • There are also important national and regional complications. France and Spain, for instance, are likely to reassess border relations at Calais and Gibraltar. For the UK, there are unique concerns facing Northern Ireland and Scotland.

Integrating defence and security into Brexit negotiations

  • Unlike in some other areas of policy, the UK is seen as a net contributor to European security and defence. This raises difficult questions for both sides about whether, when and how to leverage this in wider Brexit negotiations. Both sides risk becoming weaker and less secure if Brexit talks provoke a 'zero-sum' approach and messy divorce.

Funding for this study was provided, in part, by donors and by the independent research and development provisions of RAND's contracts for the operation of its US Department of Defense federally funded research and development centers. The study was conducted through the Defence, Security and Infrastructure programme at RAND Europe as well as through the International Security and Defense Policy Center, which is part of the RAND National Defense Research Institute.

This report is part of the RAND research report series. RAND reports present research findings and objective analysis that address the challenges facing the public and private sectors. All RAND reports undergo rigorous peer review to ensure high standards for research quality and objectivity.

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