It is remarkable that the future of defence relations between a post-Brexit UK and the EU has generated comparatively little debate. The overwhelming majority of commentators on the UK’s tortuous negotiations with the EU have focused on issues of trade, the rights of expatriate citizens, Northern Ireland and the European Court of Justice. And yet, destabilisation in both the Eastern and Southern neighbourhoods, uncontrolled migratory pressures across the Mediterranean, the war against the ‘Islamic State of Iraq and Syria’, the rising threat of terrorism and deep ambivalence about the Atlantic Alliance from within the White House have combined to make this a critical moment in Europe’s security arrangements. At a time when security and defence issues have arguably retaken centre stage in the international politics of Europe, the withdrawal of one of the EU’s major military powers from the fledgling Common Security and Defence Policy (CSDP) is a policy challenge of the first magnitude.

The UK and the CSDP

In all fairness, it should be recalled that the UK played a major role in the initial launch of the CSDP in 1999, drafting many of the foundational documents and working papers. But then the UK veered off to prioritise the UK–US relationship during the Iraq crisis of 2003 and thereafter functioned more as spoiler than driver (Howorth 2014). Despite playing a key role in the anti-piracy operation Atalanta in the Gulf of Aden, Britain’s main role over the past 10 years has been to apply the brakes—to proposals for an EU Operational Headquarters, to the funding of the European Defence Agency and above all to any expression of ambition for the future footprint of the CSDP, which London has tended to see as a potential threat to NATO. Ironically, then Prime Minister Tony Blair agreed, at the historic Franco-British summit in Saint Malo in 1998, to launch the CSDP because he was convinced that without a serious European military capacity, the Americans would begin to distance themselves from NATO. Yet, almost from the moment of the CSDP’s birth, London began to fear that its main consequence would in fact be American disengagement. Such disengagement may well be on the cards, but this would be the outcome of an internal US debate—not because of the existence of the CSDP. Growing numbers of US analysts propose a gradual US withdrawal from NATO and the transfer of leadership to the EU (Bacevich 2016; Mearsheimer and Walt 2016; Posen 2014).

Some authors have suggested Brexit will not negatively impact either the UK’s ability to continue to work with its European security partners (Menon 2016) or the effectiveness of the CSDP itself (Gros-Verheyde 2015, 2016). Others have suggested, on the contrary, that Brexit will make it extremely difficult for the UK to play a proper role in European foreign and security policy (Bond 2015; Kerr 2016), and even that it will contribute to the unravelling, not just of the CSDP, but also of the EU’s Common Foreign and Security Policy (Hillison 2016). One key analyst sees an unfolding series of post-Brexit complications which will render the future of Euro-Atlantic security cooperation highly volatile for the foreseeable future (Heisbourg 2016). It is indisputable that the withdrawal of the UK from the EU will not change the overall geostrategic situation in Europe. No challenges are going to disappear, and it is unlikely that Brexit will result in the emergence of new ones, although some have argued that both China and Russia will benefit from the destabilisation of the Old Continent that follows (Godement 2016; Nixey 2016). The main geostrategic tensions will remain.

In the year following the Brexit vote, the government of Prime Minister Theresa May was totally preoccupied with attempting to formulate a negotiating position for the coming divorce. It failed for over a year to focus on issues of security and defence, other than—maladroitly and counterproductively—appearing to threaten to leverage its defence muscle to extract concessions from the EU on other policy issues. The implied threat was that, if the EU did not make concessions to the UK on trade, the UK would refuse to cooperate on the CSDP (May 2017).

The post-Brexit ‘relaunch’ of the CSDP and the objective of ‘strategic autonomy’

The leading players in the EU, on the other hand, rapidly forged ahead with post-Brexit plans for a revamped EU strategy and common security policy. In June 2016 the EU’s much anticipated Global Strategy document (EEAS 2016) set the level of ambition for the revitalised CSDP as being nothing less than ‘strategic autonomy’ (the term appears no fewer than eight times in the document). Although the document makes no attempt to define the concept, most analysts have taken it to imply the EU’s ability to stabilise its neighbourhood without being dependent on the US. Since the Global Strategy appeared, there have been a number of potentially significant developments.

These include the decision to go ahead with a Military Planning and Conduct Capability (MPCC—the new acronym for what used to be called ‘the OHQ’); the launch of the European Defence Fund; new financial arrangements for the deployment of battle groups; and the agreement, reached at the European Council in June 2017, to operationalise for the first time the process enshrined in the Lisbon Treaty (but never hitherto acted upon) known as Permanent Structured Cooperation. How significant are these developments? The short answer is that they are helpful and creative, but they will not, in and of themselves, change anything fundamental, whether or not the UK can somehow be associated with them. There are still many obstacles standing in the way of ‘strategic autonomy’: persistent nationalist tendencies among the member states, ongoing divergences in European strategic cultures, lack of consensus about the level of ambition in this policy area, challenges to defence budgets in a time of austerity, the fetish of sovereignty, the problem of trust, the sheer scale of the challenges facing Europe in its Eastern and Southern neighbourhoods, and the absence of public awareness of and/or support for a more muscular or assertive Europe. Perhaps the biggest challenge is the parallel existence of NATO. The temptation of thinking that the new dynamic, in and of itself, is sufficient to overcome long-standing obstacles must be avoided—as must the hope (some would call it an illusion) that Brexit, in and of itself, will make some of those obstacles go away.

The UK begins to engage with the revitalised CSDP

The new defence dynamic across Europe was sufficiently robust for policy-shapers in Whitehall to conclude that the UK urgently needed to formulate proposals for its future defence relationship with the EU. On 12 September 2017 this took the shape of a 22-page paper offering a ‘future partnership’ between the UK and the EU on issues of foreign policy, defence and development. It sought to build ‘a new, deep and special partnership with the European Union’ and stated that the UK was ‘unconditionally committed’ to European security (HM Government 2017). However, the paper spends its first 17 pages stressing how important a military player the UK is, extolling the UK’s past commitment to European security and defence, and insisting that ‘the values we share are historic and deep-rooted in our societies, and the UK will always be an indefatigable advocate for them’. Only in the final few pages does the paper attempt to lay out concrete areas for a future security and defence partnership. But even here, the proposals remain devoid of all political, institutional, juridical or operational clarity. One leading observer noted that ‘one could be forgiven for thinking that this latest paper was written by a state trying to join the EU, not one trying to leave it’ (Smith 2017). Comment on the paper was universally sceptical, with ardent Brexiteers predictably seeing it as evidence that the May government had ‘walked into an EU ambush’ that would lead to Britain joining an ‘EU army’ (Gutteridge 2017).

The reality is that in September 2017 no leading UK politician, from either party, had a clear view of what sort of future defence relationship Britain might entertain with the EU. The volatility of the UK electorate, as shown in the general election of June 2017, in which Theresa May gambled on obtaining a strong mandate to negotiate a hard Brexit—and lost—made politicians wary of getting too far ahead of public opinion. In the autumn of 2017, every statement on Brexit from UK leaders, of whatever persuasion, seemed primarily aimed not at the EU negotiators, but at the UK electorate or at Tory grandees pondering the need for an alternative prime minister. Mrs May’s much-hyped ‘major policy speech’ on Brexit in Florence on 23 September was the clearest example of such coded rhetoric. The Financial Times, not known for hyperbole, passed the speech off as ‘45 min of repetitious and platitudinous abstraction [with] not a single memorable phrase’ (Leith 2017). On security and defence, the prime minister broke new ground by suggesting the need for a ‘treaty’ between the UK and the EU, but without offering the slightest clue as to what that might involve. It is therefore left to the analyst to try to imagine what the broad outlines of that future defence relationship might entail.

UK–EU defence cooperation post-Brexit: strengths and weaknesses

Let us begin on the negative side of the ledger and move towards the more positive. The UK continues to give the impression of not having realised how high the stakes are in its future defence relations with the EU. There is a general sense in Whitehall that—when it comes to defence muscle—the EU stands to lose far more from Brexit than does the UK. The British media’s obsession with the bogeyman of the ‘European army’ has always served as a smokescreen to avoid coming properly to terms with what the CSDP implies. Ever since the referendum on Brexit, Defence Secretary Michael Fallon has continued to lay out publicity-ripe ‘red-lines’, insisting that the UK will veto the formation of a ‘European army’ (Kern 2016) and arguing that ‘defense is for NATO and not the European Union’ (Deutsche Welle 2017). This approach might seem to directly contradict the spirit of the 12 September paper extolling the security values shared by the two sides. Yet that same paper stresses on numerous occasions that NATO remains ‘the bedrock of the UK’s national defence’. Cooperation between the EU and NATO has become a shibboleth echoed by almost all players across the EU. Many experts and officials across the Atlantic are currently calling for the EU to take on ever greater responsibility for the security of Europe’s neighbourhood. If the goal of ‘strategic autonomy’ is to be reached, the logic of the ‘Europeanisation of NATO’ becomes compelling (Howorth 2017). The UK’s post-Brexit role in that constructive development is likely to be highly ambivalent if not downright obstructionist. The fact that many of the remaining 27 EU member states feel ‘liberated’ by the departure of the British from the security policy sector clashes with the widespread desire across the EU to enhance relations with NATO. The eventual outcome of that relationship will determine the future of the EU defence project.

Fallon’s conviction notwithstanding, the UK–US ‘axis’ will undoubtedly be relativised by Brexit. The UK can no longer gamble on the ‘special relationship’—a relationship that, in any case, has been more talked about in London than in Washington. As long as the US (under Trump or any succeeding president) continues to see the defence of Europe as a vital strategic interest, it will have no alternative but to prioritise its relations with the EU. American officials and analysts have been saying this for years. Fallon and the Brexiteers appear not to have been listening.

Another negative on the balance sheet is the UK’s post-Brexit situation with respect to counterterrorism. As Mortera-Martinez (2017) recently stressed, this is the dominant policy issue on the security agenda. Here, the UK has a massive interest in remaining attached to Europol and to the various intelligence databases such as the Schengen Information System. But even assuming the EU27 were willing to continue to involve the UK under some associate format, they would arguably impose two major conditions, both of which would cause headaches for London. The first would be the jurisdiction of the European Court of Justice over the use of these databases. The second might be the growing reluctance of the EU27 to share data with the Trump administration, given its hostile approach to refugees and asylum seekers. The UK’s 12 September paper studiously ignores these issues and confines itself to asserting that there are ‘clear benefits for both sides in coordinating our efforts to protect our citizens’ (paragraph 70). The future role of the European Court of Justice is for most UK politicians an ongoing blind spot, if not a policy impasse.

UK defence spending is likely to tumble as a result of the economic costs of Brexit to the UK economy. The June 2017 launch of the new aircraft carrier Queen Elizabeth II—with no support vessels—drew attention to the fact that the UK’s desire to be perceived as a major projector of military power requires it to procure a full carrier-group of support and protection vessels. It is far from clear that the British will be able to afford such a capacity. The Royal Navy is currently in dire straits, with many of its surface vessels inoperable (Coughlin 2017).

On the other hand, there is evidence that the British Ministry of Defence continued to play an important role in Brussels as the European External Action Service developed its Security and Defence Implementation Plan. This is, after all, their professional bread and butter. Despite UK reservations about the finalité of the CSDP, it has always been in the UK’s interest to maximise EU defence capacity—and to prevent the EU from remaining ‘just’ a civilian power (Besch 2017). Many in London understand that this is an area where good relations with the EU can be maintained. That understanding lies at the heart of the UK’s official papers on this policy area—no matter how vacuous these might be in terms of concrete proposals. The UK defence industry (despite its global reach) also has a major interest in cooperating with its EU partners and in continuing to benefit from joint research and technology and access to EU financing, particularly under the recently launched European Defence Fund. However, recent statements from EU officials make it clear that a post-Brexit UK will not be entitled to European Commission funding for such projects. London will undoubtedly continue to fight for such access, but there are few reasons to believe that the EU will make an exception in this case.

Franco-British cooperation (the 2010 Lancaster House process) will continue, but in a different framework: the emergence of the Paris–Berlin axis. London will no longer be able to play Paris off against Berlin, especially given President Macron’s commitment both to the EU and to Franco-German leadership. The UK will find it harder to engineer multiple bilateralisms, although Sweden’s and Finland’s 2017 decision to join the UK-led Joint Expeditionary Force suggests London still has significant clout. It seems the UK has not ruled out participating in Permanent Structured Cooperation, although how that would be arranged institutionally and operationally remains unclear. There is also little clarity about future UK relations with the battle groups (the UK is scheduled to lead a battle group in July 2019, shortly after the time limit for withdrawal from the EU) or about the UK’s future relationship with the European Defence Agency.

There is political will on both sides for the UK to be as closely involved as possible with the EU in this policy area. Both sides recognise this to be in their best political and geostrategic interests. For this to become a reality, there would have to be some imagination and flexibility on the legal side. When the CSDP was launched in 1999, the EU arguably should have been far more flexible in associating Turkey and Norway with the project. But the lawyers refused. This time the politicians should urge the lawyers to find a new politico-institutional framework to maximise the involvement of the UK in the CSDP—if necessary through some form of UK associate membership of the Political and Security Committee. The same flexible arrangements could then be applied, with appropriate modifications, to countries such as Turkey and Norway. Much will depend on the atmosphere and tone of the Brexit negotiations. If this emerges as positive, then much is possible on the defence front (including UK involvement in Permanent Structured Cooperation). If the talks become embittered, defence issues will be much more difficult to resolve. At the time of writing, the EU negotiators remain frustrated at the lack of concrete proposals from London.

The one conclusion that imposes itself is that the imminent departure of the UK from the existing defence structures of the EU has opened a Pandora’s box whose eventual consequences remain difficult to foresee.


Since 1945 the UK and continental Europe have had a highly complex relationship in the field of security and defence. For 50 years (1949–99), the UK prevented Europeans from engaging in this policy area. The CSDP was launched in large part because London feared that, without it, Washington would disengage from NATO. Yet, whenever a genuine security crisis has arisen in Europe’s neighbourhood (the Balkans, Libya, Georgia, Ukraine or Syria), the EU has remained dependent on US military leadership. In 2016 three developments coincided to shift that unsatisfactory pattern: Brexit, the election of Donald Trump and the stated ambition of the EU27 to move towards strategic autonomy. The future cooperation between the EU and the UK over the definition of a new defence ambition for Europe will be difficult but crucial to the future security of the continent.