E3 Reunited: New Treaty Reinvigorates UK, Germany, and France as Core of European Security
German Chancellor Friedrich Merz visited London this week to sign a landmark UK–Germany friendship treaty with British Prime Minister Keir Starmer, following closely on the heels of French President Emmanuel Macron’s visit. These consecutive high-level engagements mark the symbolic and strategic return of the E3—France, Germany, and the UK—as a central force in European security. Despite the UK’s departure from the EU, this revived configuration could play a pivotal role in unifying Europe’s complex security architecture.
Revitalizing the UK–Germany Relationship
The Kensington Treaty represents a significant enhancement of UK–Germany bilateral ties. Before Brexit, Germany mainly engaged the UK through EU channels, except in matters of foreign and security policy. However, following the UK’s withdrawal from the EU, Berlin prioritized EU single market integrity, leading to a sharp decline in UK–Germany trade, diplomatic ties, and even educational exchanges. By 2024, the UK had fallen from Germany’s third-largest trading partner in 2016 to ninth, and student exchanges dropped by over 80%.
To reverse this decline, early efforts began under former Chancellor Olaf Scholz, whose SPD party had close ties to the UK Labour Party. In August 2024, Scholz and Starmer initiated negotiations for a broader treaty. Though these were briefly stalled due to the collapse of Scholz’s government in November 2024, the incoming administration under Merz, with SPD as a junior partner, quickly resumed the process. Merz has emphasized the UK’s importance as a security partner, especially regarding the war in Ukraine and transatlantic cooperation.
Main Pillars of the Kensington Treaty
The new treaty has two core motivations. First, it lays a broader foundation for enhanced bilateral cooperation with structured mechanisms such as biennial summits. It defines six main areas of collaboration:
- Foreign and diplomatic policy
- Defence and security cooperation
- Internal security and migration
- Economic, scientific, and research partnerships
- People-to-people exchanges
- Energy and climate policy
For the last four areas, the treaty was carefully coordinated with the EU Commission to avoid conflicts with the broader EU–UK relationship, ensuring that it complements rather than competes with EU frameworks.
The second and dominant aspect of the treaty is its strong emphasis on foreign, security, and defence policy. It commits the UK and Germany to closer coordination in NATO, the UN, and the G7, and explicitly supports a constructive EU–UK relationship.
Defence: The Heart of the Agreement
The most substantial component of the treaty builds upon the previous UK–Germany Trinity House Agreement, expanding defence collaboration significantly. Key elements include:
- Joint work on defence industrial projects (e.g., deep precision strike capability)
- Coordination on defence exports
- Cooperation on NATO’s eastern flank and in the North Sea
- A bilateral mutual defence clause, supplementing NATO commitments
These initiatives form part of a broader list of “lighthouse projects,” with defence clearly taking center stage.
Anchoring the E3 in European Security
The treaty not only strengthens UK–Germany ties but also integrates this relationship into the wider E3 framework. Notably, it calls for enhanced trilateral cooperation among the UK, Germany, and France—an unusual feature in a bilateral agreement. This completes the triangle of existing bilateral treaties: the UK–France Lancaster House Treaty, and the France–Germany Elysée and Aachen Treaties.
As a result, Europe’s three major military powers are now bound by formal agreements, allowing the E3 to act in concert. The group has already coordinated European positions on crises such as the Middle East and the Iran–Israel conflict, and expanded into the Weimar+ format (with Poland, Italy, the EU, and NATO) in response to Russia’s war in Ukraine. The UK and France have led efforts to build a “coalition of the willing” as a potential ceasefire force in Ukraine, while Germany and the UK now co-lead the Ramstein format for military aid coordination, replacing the U.S. in that role.
A Flexible Yet Fragile Architecture
The E3’s flexibility and its web of bilateral treaties are both its greatest strength and a structural vulnerability. While uniting the continent’s largest defense spenders, the E3 alone cannot fill the gaps created by Brexit between NATO and the EU. To truly serve as the backbone of European security, the format will need to broaden its engagement with partners like Poland and other NATO and EU members.