Lancaster House 2.0 and European Security: the UK and France Join Forces in Defence Investment

"The UK and France have a special responsibility for European security. Now is the time to clarify this,” declared French President Emmanuel Macron in a speech given to the House of Commons on July 8 during his state visit. At DSEI 2025 (9-12 september 2025, London), this year’s Lancaster House 2.0 agreement between the UK and France seems to have taken centre stage. The declaration, aimed at bolstering bilateral cooperation in defence and security procurement and modernisation, comes at a time when Europe faces increasing threats from Russia, amid debate over future U.S. defence priorities.

Achieving strategic autonomy requires a certain amount of multilateral—and bilateral—cohesion between the main European powers. The Lancaster House 2.0 declaration therefore comes at an opportune moment and signals a decisive attempt by Europe’s two leading nuclear powers to reassert leadership in deterrence, high-intensity conventional readiness, and defence-industrial sovereignty. With NATO recalibrating its posture after the 2022 Strategic Concept, and the credibility of the American nuclear umbrella under sharper debate, Paris and London want to demonstrate that Europe’s own security backbone rests on more than Washington’s guarantees. As the International Institute for Strategic Studies observed, Lancaster House 2.0 is “a statement of entente for wider European security.”

A shared nuclear umbrella

Front and centre of the new agreement is a striking innovation in the nuclear field. While France and the UK have long maintained separate deterrents—Paris with its force de frappe, London with its Trident-equipped submarines—the new declaration commits them to coordinated posture. It outlines future cooperation between independent nuclear deterrents by reinforcing coordination, research, nuclear doctrines, the strengthening of international non-proliferation architecture and the establishment of a “UK-France Nuclear Steering Group to provide political direction for this cooperation, led by the Presidency of the French Republic and the Cabinet Office to coordinate across policy, capability and operations.”

This Steering Board, co-chaired from the Élysée and the UK Cabinet Office, and tasked with synchronising doctrine, policy and operational readiness, represents—for the first time—a European nuclear umbrella not anchored in Washington but in London and Paris. For allies like Poland, which has openly debated whether to pursue its own nuclear capability in the face of Russian aggression, the Franco-British signal is highly significant. Former NATO official and member of the European Council on Foreign Relations thin-tank Camille Grand described this as “meaningful change” and a “powerful commitment to European security”, particularly given France’s traditional insistence on nuclear independence.

Indeed, the move represents both a significant symbol of outward evolution in French nuclear doctrine, and highlights divisions within Europe. According to Lawrence Freedman, emeritus professor of war studies at King’s College London, speaking to the Financial Times: “As far as I know, the French have never admitted publicly that they co-ordinate nuclear capabilities with anybody else, so that in itself is quite an important development.” But Germany, despite its economic heft, remains outside the nuclear club and dependent on U.S. extended deterrence. In the long term, Lancaster House 2.0 underscores that strategic leadership in Europe rests above all on Franco-British shoulders.

Corps-level warfighter

Equally transformative is the evolution of the Combined Joint Expeditionary Force (CJEF), the Franco-British formation created under the original 2010 treaties. Previously structured at division level and focused on expeditionary operations in theatres such as the Sahel or the Middle East, it is now being expanded and re-designated as the Combined Joint Force (CJF).

The CJF will represent a corps-level capability, up to five times larger than the CJEF, explicitly designed for high-intensity conflict in the Euro-Atlantic theatre. According to the joint statement, the reform refocuses the force “on the Euro-Atlantic and warfighting at scale to deter, placing it on an operational footing for the first time.” According to the UK Defence Journal, “the new CJF is framed not only as a Franco-British tool for bilateral coordination, but as an operational headquarters and reserve formation capable of augmenting NATO in a crisis.”

This change matters for three reasons. First, it will provide Europe with a deployable corps-sized formation able to operate independently or within NATO, bolstering collective defence. Second, it reflects the hard lessons of Ukraine: in a high-attrition war of manoeuvre, scale matters. Finally, it symbolises a pivot away from asymmetric expeditionary operations towards the kind of conventional, peer-to-peer warfare that is once again at the heart of European security planning. New governance arrangements will ensure shared decision-making and smoother mobilisation. This deep interoperability between Europe’s two most capable militaries is intended to reassure allies and deter adversaries simultaneously.

The “Entente industrielle”

If nuclear coordination and corps-level readiness provide the strategic framework, it is the industrial partnership that ensures credibility. Lancaster House 2.0 explicitly launches an “Entente Industrielle”, a revitalised compact to tie together the defence industries of both nations. The idea is “to enhance capability and industrial co-operation, bringing our defence industries and militaries closer than ever before to strengthen NATO,” according to the joint statement.

Central to this are missiles. MBDA’s Storm Shadow/Scalp-EGcruise missiles, combat-proven in Ukraine where they have repeatedly struck high-value Russian targets, will see their production lines expanded and upgraded. Stocks are expected to be replenished to meet the demands of prolonged high-intensity conflict, reflecting lessons from Kyiv’s struggle to secure sufficient long-range strike capability.

Beyond upgrades, the two governments have committed to accelerate the STRATUS programme. Due for delivery from 2031, this next-generation missile system will include a pair of munitions: a stealthy subsonic variant optimised for deep precision strikes against hardened land targets, and a supersonic manoeuvrable missile designed to neutralise advanced maritime and aerial threats. Together, these weapons are intended to form the cutting edge of Europe’s future strike capability, reinforcing the continuity between nuclear deterrence and conventional deep-precision strike.

Industry voices have welcomed the pact. Julie Marionneau of ADS, the UK aerospace and defence trade body, argued that "this revitalised Lancaster House agreement should strengthen cooperation between the UK and France in terms of building bilateral industrial relationships, enhancing supply chain resilience, and reinforcing the foundation for enduring security and sustainable growth across the continent.”

The Lancaster House 2.0 agreement now serves as a strategic signal that France and the United Kingdom intend to anchor European security through deterrence, readiness and industry. Coordinated nuclear postures, a deployable corps-level joint force, and an ambitious industrial agenda together amount to a blueprint for European strategic reinvention.