Ten years after the Brexit referendum: Same threats, less say

A few days before the Brexit referendum, I wrote about the troubled international environment then facing the UK, from instability in the Middle East to the crisis in Ukraine. “All of these problems are common to the UK and its EU partners,” I argued. “Not one of them would be solved, or have less impact on the UK, if Britain were to leave the EU.” 

Ten years on, that remains true. So Britain and its European partners have ended up working together more often than not – in response to Russia’s full-scale invasion of Ukraine, through successive crises in the Middle East, and as the United States reduces its contribution to Europe’s security. 

Nonetheless, Brexit has cost the UK some influence. Britain has not been able to retain the seat close to the table that then prime minister Theresa May proposed in September 2017. She wanted the option of agreeing joint positions on foreign policy issues, and the ability to work with the EU on mandate development and detailed operational planning for civilian missions and military operations under the EU’s Common Security and Defence Policy (CSDP). At the time, that was too much for the EU to swallow in the context of the mistrust and anger caused by the Brexit vote. Britain’s impending withdrawal enabled the EU to move ahead with some forms of defence co-operation that London had previously blocked, including Permanent Structured Co-operation (PESCO), which was launched in 2017 and allowed a vanguard group to move ahead with defence projects. 

Boris Johnson then decided to exclude foreign and defence policy co-operation from the Trade and Co-operation Agreement, the treaty that governs the UK’s post-Brexit relationship with the EU. The reasons were partly tactical: his team did not want to appear demandeurs for a relationship in those areas, for fear that the EU side would then demand concessions elsewhere in return. But they were also ideological – some in Johnson’s circle believed that the UK’s foreign policy relationships should be conducted with individual member-states, not EU institutions. 

“Even where strategic interests align, the mistrust of the Brexit years has not disappeared.” 

Since Brexit, and particularly since Labour took office in the UK in 2024, formal and informal contacts between the EU and the UK on foreign policy issues have increased. After Russia’s February 2022 invasion of Ukraine, Liz Truss became the first UK foreign secretary to attend an EU Foreign Affairs Council since the UK’s departure, and the two sides began working more closely to co-ordinate the now-separate sanctions regimes. David Lammy, when he became foreign secretary, agreed with Josep Borrell, then the EU’s High Representative for Foreign Affairs and Security Policy, to hold six-monthly ministerial meetings, alongside regular official-level dialogues on issues including Russia/Ukraine, the Indo-Pacific region and hybrid threats. 

The Security and Defence Partnership (SDP) agreed at the EU-UK summit in May 2025 seemed to mark a step change. Among other things, it promised further dialogues from ministerial level downwards, opened the possibility of UK participation in EU civilian and military CSDP operations, and committed both sides to explore closer links between the UK and the European Defence Agency, which could give the UK access to some EU defence capability development programmes. 

More than a year after the SDP was agreed, however, much of its potential remains unfulfilled. The foreign secretary has not become a regular attendee at EU Foreign Affairs Council meetings. Nor has the UK moved quickly to negotiate a Framework Participation Agreement to take part in EU crisis management operations. 

Most importantly, talks on British participation in SAFE, the EU’s programme for joint procurement of military systems and munitions, broke down after the Commission sought a large up-front financial contribution from Britain, and London concluded that the price was too high. The result is that one of Europe’s largest defence industrial bases remains outside an important programme designed to enhance European defence capabilities. It is a missed opportunity – and a reminder that, even where strategic interests align, the mistrust of the Brexit years has not disappeared. 

In the absence of comprehensive co-ordination through an EU framework, various bilateral and minilateral relationships have appeared or evolved, designed to enable the UK to work with its partners. These formats are a pragmatic response to the desire of many European countries to keep the UK involved in European security issues, at a time of crisis. But they can create their own problems. Some countries resent being excluded from groupings such as the E3 – France, Germany and the UK – and worry about the evolution of a directoire that shapes European foreign policy without giving the EU institutions or all member-states a voice. 

Brexit has done less damage to UK-EU co-operation on foreign and defence policy than in many other areas, partly because the EU’s Common Foreign and Security Policy remains largely inter-governmental. But that is not a reason for complacency. The UK and the EU could do more to align their responses to shared threats and to increase their co-ordination in mitigating the risks to Europe’s security. 

Brexit changed Britain’s institutional position in Europe, but it did not change Europe’s geography. What threatens the EU still threatens the UK, and vice versa.

Ian Bond is deputy director of the Centre for European Reform.

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