From awkward ex to security partner: Germany and Britain ten years after the Brexit referendum

By Nicolai von Ondarza

Ten years after the Brexit referendum, the UK has lost relevance for Germany in many policy areas. But in others, notably foreign and defence, the relations have even intensified.

When the United Kingdom voted to leave the European Union on 23 June 2016, Berlin woke to a shock the next morning. Although the polls were quite close, the overwhelming expectation was that the “pragmatic” British would, despite their long tradition of EU scepticism, vote to remain a fellow member of the EU. Over the following decade, not only did the UK leave the EU in a tumultuous process, but British-German bilateral relations also changed significantly.

The relationship developed, however, in a counterintuitive way: British-German bilateral ties suffered most during the Brexit process whilst the UK was still formally a member of the EU, also because the German government explicitly wanted to avoid making negotiating Brexit a bilateral issue. In contrast, bilateral relations first stabilised and, after EU-UK relations also improved, even entered a new phase under the 2025 Kensington friendship treaty. By June 2026, Berlin and London cooperate more deeply in some areas on a bilateral and minilateral level on questions of foreign, security and defence policy, even if Brexit has created an indisputable gap in bilateral relations, too.

Keeping the distance during the Brexit negotiations

In the initial Brexit negotiations following the referendum, the main aim of the German government was to protect the integrity of the remaining EU-27 and the single market. Whereas some Brexiteers hoped for “German car-makers” to push for a British-friendly negotiation stance, in practice the opposite happened: From 24 June 2016 onwards, the German government under then Chancellor Angela Merkel made clear that it wanted to avoid any semblance of bilateral negotiations between Berlin and London (or Paris and London) on the terms of Brexit.

Instead, it put its weight behind Michel Barnier as the common EU negotiator, insisting that all questions concerning Brexit between 2016 and 2020 be handled between the EU institutions and the UK. Within the EU-27, the German government as well as German businesses also supported a clear line of rejecting any UK attempts at cherry picking the single market. This included particularly strong support for the Republic of Ireland as an EU member with its interest in keeping the border with Northern Ireland open.

Consequently, although the UK only fully exited the EU in January 2020 (with a transition period until December 2020, until which it remained in the EU’s single market and customs union), it was during this last period of joint EU membership in which bilateral relations cooled the most. This was an explicit choice driven by Berlin who wanted to avoid a bilateralisation of the Brexit negotiations. A notable exception remained foreign, security and defence policy, where both countries – often together with France as E3 – continued their cooperation, but in other areas Berlin in particular insisted on visible distance from the UK.

From normalisation to intensification

After the UK had formally exited the EU and entered the new post-Brexit relationship with the EU, the first cautious steps to rebuild bilateral ties began. The first step was a joint declaration on foreign policy cooperation in June 2021 by the two countries’ foreign ministers. This constituted the first creation of new institutionalised ties between Berlin and London, including an annual “Strategic Dialogue” between the two foreign ministers. It was also the first of a series of bilateral agreements the UK struck with other EU countries on foreign policy cooperation. Notably, due to the continued political instability in the UK, the Strategic Dialogue not once brought the same two foreign ministers together twice in succession.

In addition, the relationship continued to be limited by the political tensions between the UK government and the EU. In particular, the threats from the government under Boris Johnson to unilaterally violate the Withdrawal Agreement with the EU over Northern Ireland were regarded in Berlin and Brussels as a significant violation of trust that also impacted the willingness to work with the UK on the bilateral level. EU-UK relations started to improve with the closer cooperation on Ukraine after the Russian full-scale invasion in 2022. The real turning point was the Windsor Framework Agreement under Rishi Sunak in 2023, which laid the tensions over Northern Ireland to rest and therefore also eased the conditions for the bilateral relationship.

Since then, supported by the 2024 election of the Labour government in the UK and the social democratic connections on both sides, the two governments have agreed a series of bilateral initiatives and agreements. After the joint declaration on foreign policy came agreements on energy and climate cooperation, in particular hydrogen and North Sea offshore wind, as well as in security and defence in the form of the 2024 “Trinity House Agreement”. Often, these also had an EU-UK element, for instance with the UK joining a memorandum of understanding for North Sea offshore wind with several EU countries and the EU institutions, or the cautious re-establishment of EU-UK defence ties by British participation in the military mobility Permanent Structured Cooperation (PESCO) project.

The Kensington friendship treaty

This path of normalisation of bilateral ties transitioned into intensification with the 2025 Kensington friendship treaty between Germany and the UK, whose negotiations started under the SPD and Labour-led governments, but were quickly picked up and concluded after the snap elections in Germany in early 2025.

In the narrative of the two governments, this first-ever friendship treaty completes a triangle of deepened bilateral relationships between Germany and France (Élysée Treaty / Aachen Treaty), France and the UK (the defence-focused Lancaster House treaties) and now Germany and the UK. For this, the treaty itself both builds upon the initiatives agreed since Brexit – in particular in foreign affairs, security and defence, as well as energy – and establishes a regular institutionalised exchange. This includes bilateral summits every two years on a government-to-government level as well as regular ministerial dialogues across the board, including a continuation of the yearly foreign minister’s Strategic Dialogue.

In policy terms, the Kensington treaty is aimed at filling areas not covered by EU-UK relations and is thus intended to complement rather than compete with them. Foreign, security and defence policy form the core of the treaty, including a bilateral mutual defence commitment. Migration and internal security are also part of the extended cooperation, an area highlighted particularly by the UK government in its public communication. Additional elements include cooperation on energy, climate policy, strengthening economic links and people-to-people contacts. To put all this into practice, the treaty is accompanied by a list of joint “lighthouse projects” which range from defence to train connections from London to Berlin or easier school trips.

Anchoring the UK in flexible formats

The policy area where the relationship has developed the most is foreign, security and defence cooperation, given the vastly changed security environment. This was not a consequence of Brexit, but still an explicit choice by both governments to continue and intensify cooperation despite Brexit. Here, in the combination of NATO, the EU-UK Security and Defence Partnership, and the bilateral Trinity House and Kensington treaties, Berlin sought to keep the UK closely integrated into European security structures. Bilateral and minilateral formats often intertwined.

Two examples underline this: First, Germany and the UK cooperated closely on support for Ukraine. By public figures, they are the two largest backers of Ukraine in Europe, and the largest overall since the US under Donald Trump reduced its direct military support to close to zero in 2025. As an expression of that, Germany and the UK took over the co-leadership of the “Ukraine Defence Contact Group” closely attached to NATO. As part of the Trinity House Agreement, Berlin and London also started work on a European deep precision strike capability that is, at least in principle, also open to other European countries.

One response to the confrontation with the second Trump administration over burden-shifting to European allies has also been a renewed focus on flexible formats with the “E3” – France, Germany and the UK – at its core. Since late 2024, Berlin in particular has preferred to work on questions of hard global security, from managing Trump and US-Russia talks to the fallout of the 2026 US/Israel-Iran war, in formats that include the UK and often are only loosely attached to EU or NATO institutions. These include the E3, the Weimar-Plus (France, Germany, Poland plus UK and sometimes Italy or Spain) and other variations of the large member states.

Outlook

The British-German bilateral relationship ten years after the Brexit referendum (and around five and a half since the actual exit) has clearly entered a new stage. There is no doubt that leaving the EU and the difficult withdrawal process itself has also left a deep mark on the bilateral relationship. There are far fewer interactions between the governments, and for many policy areas, in which the EU is the primary framework for Germany, the UK is no longer as relevant for Berlin. Direct people-to-people contacts, especially among students but also workers, have dropped significantly, for school trips by 80 percent. The UK is less important for German trade than in 2016, dropping from its 3^rd (2016) to 8^th largest export destination (2025).

On the other hand, driven both by the political commitment from both sides and by the changing security environment, there has been a willingness to first normalise and then in some areas – notably foreign, security and defence – even intensify the bilateral relationship. The Kensington friendship treaty puts the UK in an elevated position among Germany’s partners – probably, alongside Ukraine, its most regular non-EU partner at present. On core questions of European security, Berlin coordinates most closely with London and Paris.

Balancing flexible formats with the UK with a stronger geostrategic EU

Looking forward, the British and German governments have set a solid framework with the Kensington Treaty despite turbulent politics in both countries. The challenge now is to get a balance right: In the bilateral relationship, the many ambitions of the Kensington Treaty will need to be filled with life and put into practice. Early signs in the defence sector or political relations – with a failure to set up a parliamentary cooperation program between the House of Commons and the Bundestag – suggests that more than initial political will is necessary to sustain a long-term intensive bilateral relationship if the common framework of the EU is missing.

Within the broader relationship, Berlin will have to balance the ambition to integrate the UK in flexible formats with strengthening the EU in times of geostrategic rivalries. This means continuing to avoid making Brexit/EU-UK a bilateral or big three/E3 issue but rather working within the EU to continue to defend joint EU interests where necessary, and find flexible solutions in the EU-UK relationship where possible.

Nicolai von Ondarza is Head of the Research Division EU/Europe of the German Institute of International and Security Affairs (Stiftung Wissenschaft und Politik).

This article was first published in the Berlin Perspectives series of the Institut für Europäische Politik (IEP).

The Berlin Perspectives series presents analyses of Germany’s European policy to an English-speaking audience. The authors analyse German positions on current topics and debates and provide policy recommendations based on their findings.

Pictures: Flags: istock / masterSergeant [all rights reserved]; portrait Nicolai von Ondarza: Stiftung Wissenschaft und Politik [all rights reserved].