Emmanuel Macron's visit to London was not a routine state event. At the Northwood base on 10 July, the French President and British Prime Minister Keir Starmer signed the Northwood Declaration, which stipulates that the two powers will coordinate the use of their nuclear forces if Europe is faced with an extreme threat.
This gave the oldest European nuclear partnership an official political framework and raised the threshold for a joint response.
Northwood Headquarters is located north-west of London and serves as the main command centre for the British Armed Forces. The complex houses the Permanent Joint Headquarters (PJHQ), UK Strategic Command, and NATO's Allied Maritime Command, making it the operational centre for all British military operations overseas and the Alliance's main naval headquarters.
France's doctrine of absolute sovereignty dates back to the time of General de Gaulle, while Britain's deterrent power is closely linked to the American Trident missiles.
The Trident II D5 ballistic missiles are solid-fuelled, submarine-launched intercontinental-range ballistic missiles that can be launched from British and American nuclear submarines.
It’s a three-stage, inertial-guided (autonomous) missile with a range of around 7,400 km (4,000 nautical miles) with the possibility of in-flight corrections and carries multiple independently targeted warheads (MIRVs) of varying power.
In British service, they form the backbone of the nuclear deterrent on the Vanguard-class submarines, and in American service, they are on the Ohio-class submarines.
During the Cold War, the two systems never conducted joint strike planning. This declaration now offers a third model. The new Nuclear Steering Group coordinates threat assessment, patrol planning, and strategic communications, while the arsenals remain under national command.
Reducing Europe's dependence on Washington
The motive is twofold. The Russian invasion of Ukraine, with Moscow's open rhetoric regarding nuclear escalation, and the uncertainty over America's commitment to NATO in Donald Trump's second term have created a political vacuum. In this vacuum, Macron and Starmer offer an umbrella that would reduce Europe's dependence on Washington.
The agreement does not end with the strategic doctrine. The Entente Industrielle (the industrial pillar of the new British-French military-technical partnership) signed the day before provides for the joint development of a successor to the Storm Shadow cruise missile (a British-French air-launched cruise missile) and SCALP (the French designation of the Storm Shadow), beyond-visual-range air-to-air missile, and radio frequency systems to neutralise swarms of drones.
According to the Ministry of Defence, modernising the facilities in Stevenage and Bourges will sustain around 1,300 highly skilled jobs and stabilise a supply chain that has been depleted by arms deliveries to Ukraine.
Paris and London are creating a unique European high-tech munitions cluster and reducing dependence on US ITAR regulations
The planned deep strike missile will be developed as part of the Future Cruise and Anti-Ship Weapon programme (a joint UK-French project to provide a next generation of long-range missiles and anti-ship missiles) and will be compatible with next-generation unmanned aerial vehicles.
In this way, Paris and London are creating a unique European high-tech munitions cluster and reducing dependence on US ITAR regulations (International Traffic in Arms Regulations, regulations that control the export and transfer of American military technology).
The Combined Joint Expeditionary Force, which was established in 2010, is now fully operational. The expanded mandate also includes space and cyber, and it is planned to assume command of multinational operations in the first hours of a crisis within a year.
The permanent headquarters will be located in Paris, which will rotate to London after the first 12 months.
The first concrete pillar of European deterrence
The costs remain high. France spends around 5.6 billion euros a year on the maintenance of around 290 warheads. The UK, whose stockpile was recently raised to 260, realistically has around 225 warheads and has already begun replacing Vanguard-class submarines (current Trident missile carriers) with Dreadnought-class submarines (a new generation of nuclear ballistic missile submarines).
According to the Spending Review 2025, London will invest more than £6 billion in the construction of submarines and associated infrastructure over the period 2025-2029.
SIPRI (Stockholm International Peace Research Institute, an arms control research institute) warns that the global arms control system is weakening and a new arms race is already gaining momentum.
The Northwood Declaration strengthens European responsibility, but at the same time it could encourage other powers to develop their own deterrence capabilities if the transatlantic guarantees weaken.
Moscow sees the agreement as a provocation and is threatening an asymmetric response.
The Baltic states and Poland see it as the first concrete pillar of European deterrence, while Berlin, although supportive, is just opening a domestic debate on Germany's role, i.e., participation.
Brussels proposes to add a chapter on the nuclear dimension to the EU Strategic Compass 2026 (the future framework of the common security policy), which would put the topic on the EU agenda for the first time without US mediation.
Brussels expects the British-French axis to become the backbone of the European precision weapons industry
The industrial part of the agreement gains momentum with the opening of the new production lines for the Storm Shadow SCALP.
A larger series will compensate for the losses from the war in Ukraine and form the technological basis for a new deep strike missile with a range of more than 1000 kilometres. The first prototype is planned for 2028-2029.
Brussels expects the British-French axis to become the backbone of the European precision weapons industry. If the plan comes to fruition, for the first time there would be a continental chain capable of independently developing, manufacturing, and supplying strategic weapons without the USA granting licences for components.
This practically paves the way for the gradual development of the industrial base of the future European defence pact.
Who holds the other key?
In NATO, the "dual key" means that the use of a nuclear weapon requires the consent of both the United States and the host country. The London-Paris declaration introduces an additional layer of decision-making, raising the question of who holds the other key when the targets are in Europe.
Poland and the Baltic states are already raising questions about the criteria that would trigger a British or French strike to coordinate civil and missile defence plans.
If the US Congress increases guarantees to Europe, this British-French coordination could remain a political signal without full operational integration
The Pentagon publicly supports greater European responsibility, but confidential analyses warn that the new structure could undermine the existing system of control and reduce American influence in the decision-making process.
The parliamentary debates in London and Paris will show how much political capital the leaders can invest. In France, the right claims that the signing "dilutes" the doctrine of independent strike action. In the UK, the opposition is questioning whether the rapprochement with Paris represents a de facto return to common European structures after Brexit.
The financial markets are closely monitoring the budget developments in London and Paris.
The Ministry of Defence estimates that the construction of four Dreadnought-class submarines will cost around £31bn, with an additional £10bn in reserve, while the UK government plans to increase overall defence spending by around £6.4bn by the 2027/28 financial year to reach a level of 2.5% of GDP.
France is already spending around € 5.6 billion a year to maintain an arsenal of 290 warheads and is counting on exports of the new missile to cushion the surge in modernisation costs.
The Nuclear Weapons Council, which will meet quarterly, has been tasked with preparing the first joint "table-top" simulation by 2026 and subsequently a plan for practical exercises within the Combined Joint Expeditionary Force.
The European Council is considering establishing a permanent consultation channel with London and Paris by 2027 if Washington continues to focus on the Indo-Pacific region, in which case NATO would gain the first formal European pillar of deterrence within the existing Alliance framework.
If, on the other hand, the US Congress increases guarantees to Europe, this British-French coordination could remain a political signal without full operational integration.
But even this outcome redefines the debate, as European nuclear autonomy moves for the first time from the realm of hypothesis to the realm of plans, budget lines, and production orders.
It is no longer enough for Europe to discuss the role of the US in deterrence. It must now answer the question of how much risk and cost it is willing to take if the protection of its own continent depends on its decisions and not just on the transatlantic will.
