Come midnight on the eve of Brexit, British tanks will not turn into pumpkins, nor battleships into watermelons. The remaining EU Member States do not have to replace British troops, for they are not going anywhere. Britain is not going anywhere either: it will still be in Europe, and threats to Europe will remain threats to Britain. One can safely assume therefore that if a threat to European interests warrants military action, in Europe’s periphery or beyond (to protect a shipping lane, for example), the UK is more likely to be part of the action than not.

As long as we are below the threshold of NATO’s Article 5, such action can be initiated by any group of European states in a variety of frameworks: NATO, the EU (through the CSDP), the United Nations, or an ad hoc coalition. Those able and willing to act in a specific crisis will select the operational framework best suited to that crisis, in political as well as military terms.

The British contribution to CSDP operations has always been relatively limited. The UK does command the naval operation Atalanta, fighting piracy in the Gulf of Aden, from its operational headquarters in Northwood, but it doesn’t contribute any actual ships. Nevertheless, it would be logical for the UK to keep the CSDP option open, for there will be contingencies in which this will be the best suitable framework. Legally that is perfectly possible: many non-EU states take part in CSDP operations already, from close neighbours to distant partners such as Colombia. The question is whether domestic politics will allow the British government to continue its operational cooperation with the CSDP. And will the UK be satisfied with the existing arrangements for non-Member State contributions (which do not allow for much of a say in the political control and strategic direction of an operation)? If London desires an upgraded arrangement, it will have to offer something–perhaps the continued availability of Northwood, on a case-by-case basis, for CSDP operations.

The sad fact is that other EU members are not that keen on deploying troops for the CSDP either, at least not for operations at the higher end of the spectrum. In recent years, combat operations have increasingly been mounted by ad hoc coalitions outside the formal framework of both the EU and NATO. That is the case for the most important operation today, the war against IS, which is fought by an ad hoc coalition under US command. Usually just a handful of EU Member States or European Allies participate in a meaningful way, even when such a temporary coalition uses the NATO command structure, as for the Libya air campaign in 2011.

Perhaps precisely because so few participate in combat operations anyway, governments seem to prefer to avoid the more structured EU and NATO decision-making in which all have a say. Today, only training and patrolling are undertaken through the CSDP and NATO (NATO organizes deterrence, of course, and a forward presence on Europe’s eastern border, but that is under the aegis of Article 5).

Brexit may increase this tendency even more. As the UK will leave the EU, it may see an interest in deepening bilateral partnerships with those it sees as key European partners. The most important of these is France, linked with Britain through the 2010 Lancaster House Treaties on defence cooperation. Ever since, France has prioritized bilateral cooperation with the UK over the CSDP, toning down any initiatives that might jeopardize close relations with London. Even after the Brexit referendum Paris still regards the UK as its primary military partner in Europe. These are the two European countries with a global military-strategic outlook, close to full spectrum forces, and the experience of a permanently high operational rhythm. They have deployed together on many occasions, including for combat operations—that creates a strong bond.

Brexit is seen as a betrayal however, and has markedly cooled relations. Since the referendum and the publication, a few days later, of the new EU Global Strategy, France (with Germany) has taken the forefront in the EU to table renewed proposals for closer defence cooperation in the CSDP framework. Yet the suspicion lingers that in the end other EU Member States are not serious enough about defence. Ultimately therefore, the UK is likely to remain France’s military partner of choice. Too often in the past, the French have felt that they took the lead in European defence—and that, when they looked back, nobody followed (which, on occasion, was also the consequence of running ahead without telling anybody beforehand). Then again, what Paris will certainly not do is to now shift the discussion about issues of security and defence entirely to NATO.  Thus ad hoc coalitions may well remain the most common format to initiate non-Article 5 combat operations.

Chances are, though, that the UK will be so preoccupied with the fall-out of Brexit that its international presence will suffer. In fact, it already has since first the Scottish referendum and then the Brexit referendum itself forced the British government to focus on domestic politics. The actual Brexit negotiations that will start once the government decides to activate Article 50 of the Treaty on European Union will be incredibly complex. Not much bandwidth may remain to devote to other issues of foreign and security policy. Therefore, if Britain is likely to participate in the major European operations, it is far less likely to initiate them. Reactivity rather than proactivity can be expected.

Until now the Franco-British axis was the engine of Europe’s expeditionary role. The question now is, can European defence fly on one engine?

Further Reading on E-International Relations

• The European Union’s Security and Defence Policy Beyond COVID-19
• Post-Brexit EU Defence Policy: Is Germany Leading towards a European Army?
• European Defence at a Crossroads
• Brexit and the 2019 European Elections
• An ‘Expert’ Perspective on Brexit… Means Brexit
• The Decline of the SDLP and their European Election Brexit Headache