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As the United Kingdom enters a new era of strategic competition, marked by the resurgence of great power rivalry, the weaponisation of space and cyberspace, and the erosion of arms control norms, questions about how the UK manages escalation and deterrence are becoming more urgent. The Strategic Defence Review (SDR) 2025 offers an inflection point. At its core lies a critical issue: is the United Kingdom’s minimum credible deterrent posture still sufficient to navigate the complexities of 21st-century escalation where threats are increasingly multi-domain, hybrid, and unpredictable?
The Posture of Ambiguity
The United Kingdom’s nuclear posture rests on a doctrine of minimum credible capability and strategic ambiguity. It is designed to deter by creating uncertainty in the minds of potential adversaries while maintaining a deliberately limited and tightly governed force structure. Since the 1990s, British strategic doctrine has centred on a single system: a continuous at-sea deterrent (CASD) maintained through a fleet of four Vanguard-class submarines, each capable of launching Trident II D5 intercontinental ballistic missiles. These submarines, operating silently beneath the oceans, represent the final and irrevocable insurance policy against existential threats. They are, by design, invisible, both physically and strategically.
There are no air-delivered nuclear bombs in the UK arsenal. No dual-use or intermediate-range systems. No declared thresholds for use. The country’s nuclear declaratory policy remains deliberately vague, stating only that nuclear weapons would be used in “extreme circumstances of self-defence,” a formulation that intentionally leaves room for interpretation. This ambiguity is meant to complicate adversary planning and avoid setting red lines that might one day have to be crossed.
Yet ambiguity can become fragile if it is not matched by flexibility. In today’s environment, where threats emerge across domains and crises can escalate rapidly through non-kinetic means, a deterrence posture based on a single delivery system and a narrow doctrine may no longer offer the strategic leverage required.
Understanding the UK’s Escalation Ladder
Unlike some of its allies, particularly the United States, the UK does not publish a formal escalation ladder. However, one can be inferred from defence doctrine, parliamentary statements, NATO procedures, and the sequencing of historical responses to crisis scenarios.
In general terms, the UK’s escalation framework begins with political signalling and diplomatic measures. In response to provocation, and typically mobilises multilateral support through NATO, the G7, the UN, or the Five Eyes and uses public statements, sanctions, and expulsions to establish a coordinated front. Strategic messaging, both public and private, is a key early component of this framework.
Beyond this, the posture shifts to defensive military actions, such as raising readiness levels, reinforcing NATO positions in threatened regions (such as the eastern flank in the event of Russian aggression), and conducting visible force movements to deter further escalation. This also includes increasing maritime patrols and enhancing air policing missions. Simultaneously, the UK would leverage its capabilities in cyberspace. A new Cyber and Electromagnetic (CyberEM) Command, established under Strategic Command, is tasked with leading defensive cyber operations and coordinating closely with the National Cyber Force, which continues to conduct offensive and preemptive cyber campaigns. These actions, often deniable and intelligence-driven, allow the UK to engage adversaries across the digital domain, offering flexible response options below the threshold of open warfare.
Should a situation escalate further, the UK would shift into limited kinetic responses, precision strikes, special forces operations, or joint actions with allies. These scenarios could then transition further into broader conventional warfighting, involving the full mobilisation of the UK’s expeditionary capabilities, including Royal Navy carrier groups, RAF strike assets, and army battlegroups integrated into NATO structures.
The final stages of the escalation ladder involve strategic signalling around the nuclear deterrent, which may include increasing the alert status of the submarine fleet, altering patrol patterns, or referencing nuclear doctrine in diplomatic channels. In extreme cases, the UK might choose to signal its resolve through nuclear exercises, declarations of readiness, or even test launches of unarmed missiles.
What’s striking is that this ladder contains a vast leap from the realm of conventional military operations to the use of strategic nuclear weapons. There is no publicly declared sub-strategic option. No intermediate step. In this sense, the ladder has a missing rung, and that absence may itself become destabilising.
Scenarios That Test the Framework
To understand the limitations of the UK’s current posture, it is helpful to explore three illustrative scenarios. First, imagine a sophisticated cyberattack on the UK’s critical infrastructure, targeting power grids, transportation networks, and communications systems. The attack is traced to a hostile state actor but falls below the threshold of war. It causes disruption, not death. In such a case, the UK’s likely responses include offensive cyber operations, coordinated sanctions, and intelligence sharing with partners. Yet if those measures fail to deter further aggression, the following steps become uncertain. The leap to conventional retaliation risks escalation; the leap to nuclear deterrence is wildly disproportionate. The ambiguity becomes paralysis.
Second, consider a scenario in which Russia conducts a limited incursion into a Baltic state. NATO’s Article 5 would be triggered, but Moscow might bet on Western hesitation (and a more concerning thought: would the current US administration support that?). The UK would deploy forces, reinforce NATO’s eastern flank, and participate in joint planning and operations. But if Russia used low-yield nuclear weapons to de-escalate on its own terms, a doctrine it has flirted with, the UK (and potentially the US) would be left with two bad options: retaliate conventionally and risk defeat or escalate to strategic nuclear use with potentially global consequences. A sub-strategic capability would offer a third path. At present, no such path exists.
A third scenario centres on the space domain. Imagine a crisis in which a British military space asset, perhaps one supporting intelligence or early warning, is disabled by a hostile actor. This act, although non-kinetic, severely undermines situational awareness and command and control reliability. The implications are vast. Yet, once again, the UK lacks a tailored response mechanism that bridges the strategic and sub-strategic divide. The available options of diplomacy, cyber retaliation, or strategic deterrence are misaligned with the nature of the threat.
The Chasm Between Storm Shadow and Trident
The UK’s long-range precision strike capability includes both the Storm Shadow cruise missile, used by the RAF for conventional deep-strike missions, and the Trident II D5. This submarine-launched ballistic missile forms the UK’s strategic nuclear deterrent.
Between these lies the Tomahawk Land Attack Missile (TLAM), which remains in active service with the Royal Navy’s attack submarines. First introduced in the late 1990s, Tomahawk has been used in Kosovo, Iraq, Afghanistan, and Libya and is still part of the fleet’s operational inventory. Contrary to some perceptions, it has not been retired. The UK is currently upgrading its stock to the Block V variant under a £265 million contract signed in 2022. The modernised missile improves range, targeting flexibility, and survivability.
However, Tomahawk in UK service is a conventional-only system. Unlike US variants, it is not configured for nuclear payloads, nor does it maintain any dual-capable cruise missile. The UK’s nuclear deterrent remains solely delivered by submarine-launched ballistic missiles, which limits its flexibility in responding to crises that fall below the threshold of full-scale nuclear conflict.
While Tomahawk strengthens the UK’s ability to project power conventionally, it does not fill the doctrinal and deterrent gap between conventional precision strikes and strategic nuclear retaliation. That remains a core challenge as threats diversify and escalation pathways become more complex.
Rebuilding Credibility: What the Future Might Hold
Following the release of the SDR on June 2, 2025, pressure is mounting to assess whether the UK’s existing deterrence strategy can endure without meaningful adaptation. While the document reaffirmed the principle of minimum credible deterrence, it remained deliberately ambiguous on whether this posture would evolve in the face of emerging threats. That ambiguity has fuelled speculation. In the weeks since its publication, a growing number of defence analysts, military commentators, and strategic hawks have questioned whether the UK’s single-platform, submarine-based approach remains sufficient and whether future options, including sub-strategic capabilities or dual-use platforms, should now be seriously considered.
One credible future option would be the reintroduction of an air-delivered nuclear capability, restoring the sub-strategic flexibility once provided by the now-retired WE.177 free-fall bombs. While the UK has not maintained this option since their withdrawal in the 1990s, a modernised equivalent could take several forms. One route might involve developing an air-launched nuclear cruise missile, potentially integrated with future platforms such as the Tempest. Alternatively, the UK could acquire or adapt aircraft capable of deploying gravity-based nuclear munitions, such as the F-35A, which is certified to carry the B61-12 under NATO’s nuclear sharing framework.
Such capabilities would offer the UK a visible, flexible escalation option below the strategic nuclear threshold, broadening its deterrent posture without undermining the credibility of the continuous at-sea deterrent. They would also enhance alignment with NATO nuclear doctrine, providing options for burden-sharing and joint planning in theatre-based scenarios. While politically sensitive, the return of an air-delivered nuclear dimension would represent a deliberate effort to close the UK’s current gap between conventional strike and full-scale nuclear retaliation.
Hypersonic delivery systems are also under consideration, particularly through collaboration within the AUKUS partnership. These would offer rapid, hard-to-intercept strike capabilities, potentially with both nuclear and conventional variants. However, such a move would require a significant investment and risk, fuelling an arms race dynamic.
Perhaps more subtly, the UK could choose to diversify its submarine-based deterrent by developing shorter-range, lower-yield nuclear warheads for delivery by attack submarines. This option would preserve the advantages of stealth and survivability while offering a broader menu of response options. But it also blurs the line between strategic and tactical deterrence, raising complex questions about signalling and control.
Beyond platforms, the future of deterrence may also depend on the resilience of command and control systems. Investing in secure, AI-assisted decision-support tools, space-hardened communications, and survivable networks may prove just as critical as building new missiles. In a future crisis, the integrity of the UK’s NC3 (nuclear command, control, and communications) systems could be the deciding factor.
Between Modernisation and Restraint
It is worth remembering that deterrence is shaped as much by perception and intent as by raw capability. Credibility arises not simply from possessing weapons but from having the political will, strategic clarity, and operational flexibility to use them or visibly choose not to. Adding new platforms may enhance flexibility; however, such decisions must be grounded in a coherent doctrine, democratic oversight, and a clear articulation of purpose. The UK has long taken pride in its restrained and principled nuclear posture, one that balances moral responsibility with strategic necessity. Any move towards sub-strategic systems or dual-use delivery mechanisms must be accompanied by credible guardrails encompassing legal, ethical, and strategic considerations.
More is not always better. But credibility is always essential.
Conclusion: Redrawing the Ladder
The UK’s current nuclear deterrent remains potent but narrow. In a world of cyber sabotage, grey-zone incursions, and the militarisation of space, the old assumptions of linear escalation may no longer hold. Deterrence today cannot afford to be static, particularly when the next confrontation may begin not with missiles but with malware, jamming, or more little green men. In that context, a response based solely on submerged ballistic systems, which are silent, unseen, and strategically opaque, may no longer offer the reassurance or credibility it once did, whether to allies, adversaries, or the British public.
To deter in the 2030s and beyond, we must ask more complex questions. Not simply about how many warheads it holds but about how flexible, survivable, and strategically legible its posture truly is. A credible deterrent must signal strength, not confusion; resilience, not rigidity. Invisibility has served as a guarantor of second-strike assurance; however, in an era of transparency, AI-enabled targeting, and contested space, invisibility alone may no longer provide reassurance.
This piece isn’t a call for nuclear expansionism. It is a call for strategic clarity. For options that are coherent, proportionate, and tailored to a world where the battlefield may begin in space, in cyberspace, or the grey shadows between states and proxies.
The ladder of escalation has changed. It’s time to build the missing rungs with care, with clarity, and with the confidence that credibility is still the cornerstone of deterrence.
This article reflects the views of the author alone and is written in a personal capacity. It does not represent the views of any employer, institution, or affiliated organisation. The analysis is based on the open-source material and public-domain discourse at the time of writing.