What should Britain do to better extend its nuclear deterrent to European allies?
The Big Ask | No. 14.2025
Since Donald Trump began his second term as President of the United States (US), European allies have started to ask legitimate questions about whether they can still depend on America’s nuclear umbrella, which has deterred threats to the North Atlantic Treaty Organisation (NATO) for decades. This comes at a time when Russia has become a particularly malevolent and unpredictable force under the determined – but opportunistic – leadership of Vladimir Putin.
Not unsurprisingly, Europeans are starting to call for the United Kingdom (UK) and France – NATO’s European nuclear powers – to step up. Therefore, for this week’s Big Ask, we asked seven experts: What should Britain do to amplify and better extend its nuclear deterrent to European allies?
Senior Research Fellow, Polish Institute of International Affairs and Senior Lecturer, Warsaw School of Economics (SGH)
The irreducible limit to the effectiveness of defence efforts undertaken by the countries of NATO’s eastern flank has been Russia’s capability to back its nuclear threats with action, especially in the case of an absence of an allied nuclear umbrella. In this context, Poland views the US as the principal provider, whereas the British and French arsenals have generally been perceived as the ultimate tool of these countries’ self-defence. Should Central and Eastern European countries be forced to revisit the nuclear trilemma (i.e., deterrence against Russia versus strategic stability versus non-proliferation), Poland would opt for joining a nuclear sharing programme.
It seems that, at the present levels of defence spending – even at 2.5% of Gross Domestic Product (GDP) – Britain struggles to field land forces with credible expeditionary potential, to build up and modernise its air forces and navy, and to renew its nuclear deterrent. Considering Poland’s focus on the expansion and modernisation of its land forces and air-defence systems, Britain’s efforts would be particularly complementary and useful if directed at expanding its nuclear arsenal while making it considerably more flexible in terms of capabilities and doctrine of use (i.e., beyond strategic deterrence to address Russia’s escalation ladder capabilities). The considerable cost of such an expansion could be offset by creating a British-led nuclear sharing programme, which could be built around the basis of F-35A Joint Combat Aircraft as a common platform. This issue could be included in the current negotiations concerning the second British-Polish bilateral defence treaty in a decade.
Senior Geopolitical Analyst, Geopolitical Futures and Senior Fellow for Eurasia Programme, Foreign Policy Research Institute
British officials emphasise that the UK’s deterrent ‘is assigned to the defence of NATO’ already, and contributes to European security. The pressure on both Britain and France to come forwards with concrete guarantees will only increase. However, it is much easier for France to extend nuclear deterrence to the rest of Europe than it is for the UK due to British reliance on the US.
Britain’s nuclear doctrine has evolved into a posture centred on last-resort national survival. Its current force – streamlined, modernised and based solely on the Trident system – is effective as part of a wider, US-led NATO umbrella. If this umbrella recedes, it could mean the UK needs to raise its nuclear profile, increasing warheads and eventually adjusting doctrine to cover allies. But this is not a solution which would work in the short term.
Thus, Britain’s likely response to a hypothetical US withdrawal from NATO would be a combination of the following: doubling down on its own nuclear deterrent (to ensure credibility), seeking closer European defence integration, especially with France and Germany (the UK and France together would present a formidable – but not fully sufficient – deterrent without Germany upping its game too, even if only in conventional terms) and urging remaining NATO members to strengthen their militaries significantly as well.
Diplomatically, the UK should stress the enduring importance of NATO’s core mission and seek to preserve as much US engagement in Europe for as long as possible. For Britain, maintaining a strong transatlantic relationship is not just about collective security, it is a matter of strategic necessity. Closer diplomatic coordination with Washington would strengthen European deterrence while also helping the UK safeguard its global posture and long-term interests within the bilateral relationship.
Research Fellow and Head of the Deterrence and Proliferation Programme, Security Studies Centre, French Institute of International Relations
The UK should reinforce its nuclear deterrence posture by clarifying its declaratory policy, explicitly integrating the vital interests of European allies into its deterrence framework. While NATO remains the cornerstone of extended deterrence, Britain should also engage bilaterally and through small multilateral formats to reassure allies.
Closer cooperation between France and the UK is essential. The Lancaster House and Teutates treaties already facilitate nuclear collaboration, but a joint declaration affirming both nations’ commitment to European security would send a powerful signal. Britain must also ensure the robust modernisation and maintenance of its sea-based deterrent, addressing the strain on nuclear-powered ballistic missile submarine (SSBN) patrols and considering greater independence from the US for the sustainment of missiles. Exploring a renewed airborne component – or integrating Royal Air Force (RAF) forces into France’s Poker-2025 nuclear deterrence exercises – could further strengthen credibility.
Beyond nuclear capabilities, the UK should invest in conventional deterrence to maintain a high nuclear threshold, enhancing cyber resilience, deep precision strike capabilities and integrated air and missile defence (IAMD). Strategic coordination with the US remains key: linking European and Indo-Pacific stability will help sustain American commitment to European deterrence. Finally, Britain and France must present a unified stance on arms control, ensuring any US-Russian agreement does not undermine their own independent deterrents.
Dr Karl-Heinz Kamp
Associate Fellow, German Council on Foreign Relations
With President Trump having weakened US nuclear commitments, NATO’s European pillar has two additional nuclear powers at its disposal – France and the UK. Although their nuclear arsenals are relatively small, they still serve as a deterrent – both nations present an aggressor with independent nuclear decision-making centres which must be considered.
To enhance the credibility of this deterrence signal, two key elements are required. Firstly, nuclear cooperation between the two countries – as outlined in the Lancaster House treaties – must be deepened and extended to encompass sensitive issues such as nuclear doctrines and targeting. Secondly, the UK should accept France’s proposal for a nuclear dialogue with non-nuclear European states, thereby presenting a unified stance of resolve and determination towards Russia.
This dialogue should also explore potential contributions from non-nuclear states. Notably, as early as 2017, the German Bundestag’s Scientific Service concluded that Germany is legally able to provide financial support for its allies’ nuclear deterrence capabilities. Such co-financing, if undertaken by multiple nations, would ease the nuclear budgets of London and Paris significantly. In return, both countries would need to offer nuclear commitments to their allies. This approach would bolster European nuclear deterrence while maintaining the (currently still existent) American nuclear umbrella.
Tony Lawrence
Head of Defence Policy and Strategy Programme, International Centre for Defence and Security
Officials and analysts in the Baltic region place great value on nuclear deterrence against Russia, and have seen the US as its most credible and trustworthy provider. For the UK to extend credible nuclear deterrence to its European allies, it would first need to revisit its nuclear doctrine. Its declared policy of assigning nuclear forces to the defence of NATO (unless supreme national interests require otherwise) is weak compared to the solid and explicit commitment to extended deterrence which the US has made in successive Nuclear Posture Reviews.
Secondly, it would need to review its capability. The UK reportedly has up to 120 warheads available for deployment at any one time, far behind the approximate 1,700 which could be deployed by either the US or Russia. The disparity is simply too large for credible deterrence. Furthermore, while the deterrent is operationally independent, the fact that US support is essential to maintaining the Trident system also weakens credibility. For the long term, Britain would need to develop domestic industrial capacity or partner with another ally. Finally, if the UK were to mirror the American practice of stationing nuclear weapons on allied territory – arguably important to strengthening extended deterrence – it would need to complement Trident with land or air-based components.
All this would be expensive, and perhaps only achievable through some kind of Europeanisation of the national deterrent.
Doctoral Research Fellow, Oslo Nuclear Project
Emmanuel Macron, President of France, has proposed extending France’s nuclear protection to other European nations, an initiative which could be complemented by British participation. Andrzej Duda, President of Poland, and Friedrich Merz, incoming Chancellor of Germany, have both expressed interest in plans to extend British and French nuclear deterrence across Europe. While doing so would amplify the UK’s political and defence impact, the big question of whether these nuclear weapons would be sufficient to deter Russia and reassure European allies remains.
Reassuring allies is harder than deterring adversaries. In this case, while political resolve or willingness can be signalled, the limits in capability in relation to the adversary are going to play a detrimental role. Instead of launching a full-scale invasion, Russia is more likely to challenge NATO by pressuring a Baltic state while using nuclear threats to discourage an allied response. In such a scenario, it would be difficult for Britain and France to threaten strategic nuclear retaliation credibly, revealing gaps in how European allies coordinate their deterrence posture. If the UK wants to extend its nuclear deterrent to Europe, it needs to back that promise with clear policy, visible capability and consistent messaging. If any aspect feels uncertain – such as whether Britain would actually act in a crisis – it risks sending mixed signals. That kind of doubt could shake allied confidence and tempt adversaries to test boundaries.
Beyond military capabilities, there is a pressing political need for better coordination. European states should establish a dedicated forum for deterrence planning. The UK should discuss how to handle deterrence, conventional defence and emerging hybrid threats with its European partners: France, Germany, Poland and others. By coordinating on these fronts, Britain has the potential to help build a stronger, more resilient European security framework.
Senior Research Fellow at Egmont and Associate Professor at the VUB Centre for Diplomacy Security and Strategy
The UK’s nuclear deterrent forms a key part of NATO’s collective defence. It complements the extended nuclear deterrence provided by the US, complicates adversarial calculations as a second centre of decision making and greatly amplifies Britain’s influence in NATO Nuclear Planning Group consultations. In this respect it is different from the French Force de dissuasion, which is conceptually grounded in a deep mistrust of the indivisibility of the alliance’s security.
The core problem facing NATO’s nuclear deterrence today concerns the extent to which Russia seeks to distil coercive value out of its tactical and theatre-level nuclear capabilities in support of its conventional and hybrid operations. In essence, Russia instrumentalises the nuclear advantage it holds at the non-strategic level to help advance its aggressive policy aims below the nuclear threshold, and to mitigate the conventional force disadvantage it might face in a direct confrontation with NATO.
To strengthen the nuclear protection offered to its allies, the UK must get back into the business of fielding non-strategic and low-yield nuclear capabilities complementing its strategic nuclear forces. Such capabilities constitute a less devastating – but more credible – response option to meet any limited nuclear use scenarios contemplated by Russia to intimidate NATO into paralysis. As such, it becomes less likely that the nuclear threshold will ever be crossed.
The fastest way for Britain to do so would be to acquire nuclear-capable F-35A fighter jets and re-endow the RAF with a nuclear strike mission akin to that of other NATO Dual Capable Aircraft operators. Other ways of doing so would include re-introducing nuclear low-yield ground-launched cruise or ballistic missile options. Such changes would help offset the nuclear advantage which Russia currently holds and – more importantly – erode the confidence Moscow can have about the management of escalation dynamics.
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