We use cookies where necessary to allow us to understand how people interact with our website and content, so that we can continue to improve our service.
We only ever receive anonymous information, and cannot track you across other websites.
View our privacy policy
The United Kingdom’s policies and practices regarding nuclear transparency combine selective disclosure with deliberate ambiguity. This approach is shaped by two factors: first, a political commitment to demonstrate what it considers to be a responsible approach to its commitments as a ‘nuclear weapon state’ as defined in the Nuclear Non-Proliferation Treaty (NPT); and second, a strategic commitment to protecting the operational secrecy of a small nuclear arsenal built around a single delivery system.[1]
After the Cold War, the United Kingdom increased its level of transparency on warhead ceilings, warhead reductions, and the number of nuclear-armed, submarine-launched ballistic missiles (SLBMs) held or deployed. This trend reversed in the 2021 Integrated Review, marking a shift towards reduced transparency, justified by the government as necessary in a deteriorating security environment.[2] The United Kingdom discloses very little about strategic or ‘sub-strategic’ warhead yields.
The United Kingdom is, however, transparent about its headline nuclear modernisation plans based on procurement of four Dreadnought-class, nuclear-capable ballistic missile submarines (SSBNs), participation in the US Trident II (D5) SLBM life extension programmes, development of a new A2 (‘Astraea’)/Mk7 nuclear warhead, and large-scale modernisation of its nuclear weapons complex.[3]
In terms of fissile material production for explosive purposes, the United Kingdom ended this in 1995 and published historical production accounts for plutonium (2000) and highly enriched uranium (2006).[4] These have not been updated since then. The United Kingdom does, however, provide comprehensive annual reporting of civil fissile material holdings to the International Atomic Energy Agency under its Voluntary Offer Safeguards Agreement,[5] and Additional Protocol.[6] The United Kingdom also confirms its continued adherence to its moratorium on fissile material production. Transparency about facilities is also relatively strong, including historical disclosures about production and reprocessing sites at Capenhurst, Sellafield, Calder Hall, and Chapelcross.[7]
Regarding nuclear doctrine, the United Kingdom partially discloses this, stating publicly that nuclear weapons would be used only in extreme circumstances of self-defence, including defence of NATO allies. It emphasises a deliberate choice to remain ambiguous about the specific conditions in which it would consider nuclear use, and the scale of use. The United Kingdom rejects a no-first-use policy but incorporates language from the 1996 International Court of Justice advisory opinion. It also provides negative security assurances for non-nuclear weapon states party to the NPT, with conditions related to compliance and the impact of emerging technologies.[8]
The United Kingdom does not disclose the role of artificial intelligence or strategic non-nuclear technologies in its nuclear decision-making or operations, although it has affirmed in multiple venues that human political control of UK nuclear weapons decision-making will be maintained at all times. Government responses in parliament emphasise safety, responsibility, and ongoing risk assessment rather than a clear operational doctrine.[9]
In the area of pre-notifications, UK practices are mixed. The United Kingdom fully participates in international pre-launch notification systems for missile and space launches through the Hague Code of Conduct and provides reporting to the United Nations for space objects. It does not issue pre-notifications or public disclosures for nuclear-related military exercises or submarine activities. Transparency here is multilateral and technical, rather than political or operational.[10]
Overall, the United Kingdom sees transparency as important for demonstrating ‘good citizenship’ as a nuclear weapon state within the NPT, particularly in multilateral forums, while perceiving any increase in operational transparency as detrimental to the credibility of its nuclear deterrent threat. The result is an approach of relative openness about the broad structures, history, and modernisation of its nuclear arsenal and wider nuclear weapons complex, whilst remaining deliberately and openly opaque about quantitative details, operational practices, and the effects of emerging and disruptive technologies.
The UK government does not disclose its total number of nuclear-capable delivery vehicles, which consist solely of the Trident II (D5) submarine-launched ballistic missile (SLBM), deployed on the UK’s fleet of four Vanguard-class, nuclear-capable ballistic missile submarines (SSBNs).
The 2021 Integrated Review stated that the government intended to extend its ‘long-standing policy of deliberate ambiguity and no longer give public figures for our operational stockpile, deployed warhead or deployed missile numbers.’[8] Shortly thereafter, the government stated that the United Kingdom ‘has sufficient Trident II D5 missiles for its needs’.[9]
The 2025 Strategic Defence Review and the 2025 National Security Strategy provided no details on missile numbers or deployments.
The United Kingdom originally purchased title to 65 Trident SLBMs from the US under the 1963 Polaris Sales Agreement, amended for procurement of Trident in 1982.[1][10] This was reduced to 58 in 1998.[2] The missiles are designed, produced, stored, and maintained in the United States when they are not deployed on the UK’s fleet of four Vanguard-class SSBNs. The United Kingdom pays an annual contribution to the United States to support ongoing maintenance of the missile stock.[3]
Some UK missiles have been used in live test fires - eleven as of January 2017.[4] Each Vanguard submarine underwent a Demonstration and Shakedown Operation (DASO) upon commissioning, culminating in a live test fire of an unarmed Trident missile at the US missile test range at Port Canaveral, Florida. The process is repeated after each submarine is recommissioned into operational service following a multi-year mid-life overhaul and refuelling.
In 2010 the government’s Strategic Defence and Security Review stated it was reducing ‘the number of operational missiles on the Vanguard-class submarines to no more than eight’ but gave no further details.[5] This statement was repeated in the 2015 Strategic Defence and Security Review.[6]
Last updated: 22 April 2026 18:43
The UK government has disclosed that the country has one nuclear weapons delivery system, comprising US Trident II (D5) Submarine-Launched Ballistic Missiles (SLBMs) deployed across a fleet of four UK Vanguard-class, nuclear-capable ballistic missile submarines (SSBNs). The UK government has publicly stated that the Vanguard-class SSBNs will be replaced in the 2030s with four Dreadnought-class SSBNs currently under construction.[1][5]
The UK government has also publicly disclosed that it participated in the US programme to upgrade the Trident II (D5) SLBMs to the D5LE (Life Extension) version([2]. The US has now embarked on a second life extension programme (D5LE2) to extend the life of the missile to the 2080s.[3]
The United Kingdom’s last air-launched nuclear weapons (WE177 gravity bombs) were withdrawn from service in 1997.[4] The United Kingdom does not currently deploy any other types of nuclear weapons or any other nuclear delivery vehicles. On the planned acquisition of F-35A nuclear capable jets, see the data on ‘modernisation plans’.
Last updated: 22 April 2026 18:43
The United Kingdom no longer operates any fissile material production or reprocessing facilities for nuclear weapons purposes. The government announced in April 1995 that it ‘had ceased the production of fissile material for explosive purposes.'[1]
Production of HEU for defence programmes at the Capenhurst Plant in the United Kingdom ended in 1962. Since then, the country has received HEU for both its warhead programme and naval reactor programme through exchanges of special nuclear material with the US Department of Energy under the 1958 Mutual Defence Agreement. In the 1960s, the Capenhurst plant was modified to produce low-enriched uranium (LEU) for civil nuclear power reactors until it ceased operations in 1982.[2]
The UK has operated three reprocessing facilities at its Sellafield nuclear site: the First Generation Reprocessing Plant (B204), operating from 1952 to 1964, extracted plutonium from spent nuclear fuel for the UK nuclear weapon programme. It was replaced by the Magnox Reprocessing Plant (B205), which operated from 1964 to 2022. The Magnox Reprocessing Plant reprocessed spent fuel from UK Magnox nuclear reactors for civilian purposes until 2022 and for military purposes until 1995. It is now in cleanup/decommissioning. The Thermal Oxide Reprocessing Plant (THORP) was a civil reprocessing plant that operated from 1994-2018 but did not separate plutonium for the UK nuclear weapons programme.[3]
The Calder Hall Magnox power station at the Sellafield site, consisting of four dual-purpose reactors, began operations in 1956 for commercial electricity generation and plutonium production for defence needs. The Chapelcross power station in Southern Scotland operated on the same basis as Calder Hall from 1958.
Following the UK government’s announcement in 1995 that it would end production of fissile material for the nuclear weapons programme, the Calder Hall reactors were brought under Euratom safeguards and made liable to inspection under the terms of the safeguards agreement between the United Kingdom, Euratom and the IAEA.[1] Calder Hall closed in 2003.
Chapelcross reactors continued to produce tritium for nuclear weapons and were not subject to international safeguards inspection. However, the 1998 Strategic Defence Review announced that all reprocessing of spent fuel from defence reactors at Chapelcross would in future be conducted under Euratom safeguards and made liable to inspection by IAEA.[4] Chapelcross ceased operations in 2004.
Last updated: 22 April 2026 18:43
The United Kingdom partially discloses its holdings of low-enriched uranium, highly-enriched uranium (HEU), and plutonium. The country stopped production of fissile material ‘for explosive purposes’ in April 1995.[1] In 2000, it published a historical accounting of its plutonium production for defence purposes up to 1999.[1] And in 2006, it published a historical accounting of its HEU production for defence purposes up to 2002.[2] It has not subsequently updated these reports.
The United Kingdom reports to the International Atomic Energy Agency (IAEA) under three frameworks: a Voluntary Offer Safeguards Agreement (VOA);[4] an Additional Protocol;[5] and voluntary transparency commitments. The United Kingdom also publishes annual disclosures of nuclear material withdrawn from safeguards and the reasons why.[7]
Under its VOA, the United Kingdom provides two annual reports to the IAEA. First, a Material Balance Report of holdings of civil HEU and civil depleted, natural, and low-enriched uranium. And second, a Physical Inventory Listing, which catalogues all nuclear materials present at each nuclear facility at the time. The United Kingdom also reports regularly on changes in civil fissile material holdings, typically monthly.[4]
Under the UK-IAEA Additional Protocol,[5] the UK government reports, usually annually or in event-based declarations, on nuclear fuel-cycle R&D, uranium mining and milling, nuclear-related manufacturing, exports/imports of sensitive equipment, and site-level information on nuclear locations. It also grants IAEA inspectors complementary access to fuel-cycle facilities and locations.
As a voluntary measure under IAEA Guidelines for the Management of Plutonium (INFCIRC/549), the United Kingdom reports annual declarations of its civilian plutonium.[3] These voluntary guidelines were established in 1998, and participating states publish annual, public figures for civil unirradiated plutonium (plus an estimate for plutonium in spent fuel). Some states, including the United Kingdom, choose to add civil HEU figures for greater transparency.
In 2010, the United Kingdom reiterated that it was under no obligation to report the production, transfer, or use of fissile material for defence purposes to the IAEA because such material is outside the international safeguards regime.[8] It is subject, however, to a strict internal materials accountancy regime.[6]
Last updated: 22 April 2026 18:43
There is no official UK government statement, parliamentary record, or defence policy document that describes the application, limits, or governance of artificial intelligence in relation to the UK’s nuclear command, control and communications system (NC3); early-warning or decision-support systems; or the development, targeting, or employment of nuclear weapons.
However, the UK government’s 2022 Defence Artificial Intelligence Strategy stated that the UK ‘must shape global AI developments to promote security, stability and democratic values’ and that ‘We will ensure that – regardless of any use of AI in our strategic systems – human political control of our nuclear weapons is maintained at all times. We strongly encourage other nuclear states to make a similar commitment.’[1] This was reiterated in 2023.[2]
In 2025, the UK government was asked in parliament ‘if artificial intelligence has been used to support (a) routine operations and (b) policy in relation to nuclear capability.' It replied, ‘The delivery of defence capabilities enabled by artificial intelligence (AI) will be ambitious, safe and responsible. Research to identify, understand, and mitigate against risks of applying AI for sensitive defence affairs is underway. Routine nuclear deterrence operations continue to be conducted in accordance with the highest standards and controls. Regardless of any potential application of artificial intelligence in our strategic systems, we will ensure human political control of our nuclear weapons is maintained at all times.'[3]
In December 2023, the UK House of Lords Committee on ‘Artificial Intelligence in Weapon Systems’ published its report, ‘Proceed with Caution’.[4] The report noted that a key element in regulating autonomous weapons systems ‘will be prohibiting the use of AI in nuclear command, control and communications’ (p. [4]. In its response to the report, the UK government added ‘The UK is at the forefront of work internationally to reduce the risk of nuclear conflict and enhance mutual trust and security, and will continue to promote and engage with international dialogue aimed at identifying and addressing crucial AI-related strategic risks.'[5]
Last updated: 22 April 2026 18:43
The UK government has disclosed its high-level plans and a strategic rationale for modernising its nuclear arsenal, but has simultaneously increased ambiguity around its operational details in recent years.
The United Kingdom states it must modernise its nuclear arsenal in direct response to a ‘deteriorating security environment’. The 2023 Integrated Review Refresh asserts that the international context is more competitive and dangerous than at any time since the Cold War. It cites an ‘acute threat’ from Russia, an ‘epoch-defining and systemic challenge’ posed by China, and the proliferation of nuclear weapons and disruptive technologies by states like North Korea and Iran.[1]
Public, headline plans for modernising UK nuclear weapon systems and the nuclear weapons complex include:
— Building four new Dreadnought-class nuclear-armed ballistic missile submarines (SSBNs) to replace the current four Vanguard-class SSBNs, with the first-in-class HMS Dreadnought due to enter service in the early 2030s.
— Deploying on the Dreadnought SSBNs the US-designed and built Trident II D5LE submarine-launched ballistic missile (SLBM), as currently deployed on the Vanguard-class, to be replaced by the D5LE2 from the 2040s.[2][5]
— Purchasing twelve F-35A aircraft from the US to provide a ‘dual-capable’ (conventional and nuclear) air-launched nuclear capability using B61-11 US gravity bombs in support of NATO.
— Designing a replacement warhead, known as Project Astraea (A21/Mk7), in close coordination with the US W93 warhead programme to replace the current UK design (Holbrook/Mk4A).[3]
— Undertaking a massive, multi-billion-pound infrastructure modernisation initiative to support the design and production of a new warhead. This includes the Project MENSA warhead assembly/disassembly facility at the Atomic Weapons Establishment (AWE) Burghfield site; a High Explosive Fabrication Facility; and the Future Materials Campus (FMC) to manufacture, store, and recover nuclear materials for warhead components at AWE Aldermaston.[4]
— Modernising all parts of the nuclear weapons complex, including BAE Systems’ shipyard in Barrow-in-Furness, the next generation of facilities at Rolls-Royce’s Raynesway site in Derby, and the Royal Naval Armaments Depot (RNAD) Coulport, to build new facilities to support Astraea.[4]
— Exploring options to re-establish a nuclear fuel cycle for reactor fuel for defence purposes.[4]
However, very little detail has been disclosed on the capabilities, timelines, and decision-making on these projects.
The UK has maintained a moratorium on fissile material production for weapons purposes since 1995. New facilities at AWE are not for producing new plutonium or uranium. The modernisation programme involves using the UK’s existing stocks of fissile material.
Last updated: 22 April 2026 18:43
The UK government reiterated in 2021 that ‘The UK will not use, or threaten to use, nuclear weapons against any non-nuclear weapon state party to the Treaty on the Non-Proliferation of Nuclear Weapons 1968 (NPT). This assurance does not apply to any state in material breach of those non-proliferation obligations. However, we reserve the right to review this assurance if the future threat of weapons of mass destruction, such as chemical and biological capabilities, or emerging technologies that could have a comparable impact, makes it necessary.’[1]
This followed on from a 2015 statement that ‘The UK will not use, or threaten to use, nuclear weapons against any Non-Nuclear Weapons State party to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). This assurance does not apply to any state in material breach of those non-proliferation obligations. While there is currently no direct threat to the UK or its vital interests from states developing weapons of mass destruction, such as chemical and biological capabilities, we reserve the right to review this assurance if the future threat, development or proliferation of these weapons make it necessary.’[2]
In 2010, the UK government had stated that ‘We are now able to give an assurance that the UK will not use or threaten to use nuclear weapons against non-nuclear weapon states parties to the NPT. In giving this assurance, we emphasise the need for universal adherence to and compliance with the NPT, and note that this assurance would not apply to any state in material breach of those non-proliferation obligations. We also note that while there is currently no direct threat to the UK or its vital interests from states developing capabilities in other weapons of mass destruction, for example chemical and biological, we reserve the right to review this assurance if the future threat, development and proliferation of these weapons make it necessary.'[3]
Last updated: 22 April 2026 18:43
The UK government does not set out specific conditions in which it would consider using nuclear weapons but says that it would do so ‘only in extreme circumstances of self-defence, including the defence of our NATO Allies.’[1]
The language of ‘extreme circumstances’ reflects wording in the 1996 Advisory Opinion of the International Court of Justice (ICJ) on the Legality of the Use or Threat of Use of Nuclear Weapons, which stated the ICJ ‘cannot reach a definitive conclusion as to the legality or illegality of the use of nuclear weapons by a State in an extreme circumstance of self-defence, in which its very survival would be at stake.'[2] In a 2006 statement, the UK government explicitly addressed the ICJ Advisory Opinion and noted, ‘The threshold for the legitimate use of nuclear weapons is clearly a high one.'[3]
However, the 2025 Strategic Defence Review affirmed, ‘The UK is deliberately ambiguous about precisely when, how, and at what scale it would contemplate the use of nuclear weapons. The UK does not publicise figures for its operational stockpile, deployed warhead, or deployed missile numbers. This posture enhances its deterrent effect by complicating the calculations of potential aggressors and reduces the risk of deliberate nuclear use by those seeking a first-strike advantage.’[8]
The United Kingdom eschews language of ‘sub-strategic’ nuclear use, stating that ‘the UK’s nuclear weapons are not designed for military use during conflict but instead to deter and prevent nuclear blackmail and acts of aggression against our vital interests that cannot be countered by other means’.[4] It asserts that UK nuclear weapons are a tool that aims ‘to deter the most extreme threats to our national security and way of life, and that of our NATO Allies, rather than a warfighting capability intended to achieve a tactical or battlefield military advantage in a conflict.’[5]
Finally, the UK government, like NATO, does not rule out the first use of nuclear weapons,[6] because ‘the credibility of the deterrent rests on the conviction that we would bring all means to bear to ensure the security of the UK and our allies.’[7]
Last updated: 22 April 2026 18:43
The UK participates in multilateral transparency arrangements, mainly through the Hague Code of Conduct against Ballistic Missile Proliferation (HCOC), which commits participating states to provide pre-launch notifications of any ballistic missile or space launch vehicle launches and annual declarations of ballistic missile and space launch policies.[1]
Notification is sent to the HCoC’s Immediate Central Contact (ICC) managed by Austria. This includes information such as the generic class of the missile, the planned launch window, the launch area, and the planned direction. This data is shared with all other HCoC subscribing states through a dedicated online platform.
The UK provides post-launch notification to the United Nations of space launches under the 1975 Convention on Registration of Objects Launched into Outer Space. The UK also issues Notices to Airmen (NOTAM)s and marine hazard area notices for rocket launches from UK Space Agency-licensed sites.
The UK does not issue public or international pre-notifications for patrols of its nuclear-capable ballistic missile submarines, training related to the Trident nuclear weapon systems, or joint NATO nuclear exercises such as the annual Steadfast Noon exercise. However, NATO does issue public statements on military exercises, including exercises involving nuclear assets.[2]
Last updated: 22 April 2026 18:43
The UK government does not disclose in detail how it accounts for or would respond to strategic, non-nuclear technologies (for example, cyber capabilities, anti-satellite weapons, hypersonic or precision-strike systems) in its doctrine governing the employment of nuclear weapons.
However, the United Kingdom does acknowledge that emerging strategic, non-nuclear technologies could influence its nuclear deterrence posture and might, in extreme circumstances, affect the conditions under which it would consider nuclear use. In 2021, the UK government stated it reserved the right to review its negative security assurance in light of ‘emerging technologies that could have a comparable impact’ to a weapon of mass destruction. It reiterated that it will remain deliberately ambiguous about precisely when, how and at what scale it would contemplate the use of nuclear weapons.[1]
Last updated: 22 April 2026 18:43
The UK government does not disclose an exact, total number of nuclear warheads in its stockpile. Instead, it has regularly disclosed a ‘warhead ceiling’. The most recent disclosure was in the 2021 Integrated Review of Security, Defence, Development, and Foreign Policy. This stated that ‘in recognition of the evolving security environment, including the developing range of technological and doctrinal threats,’ the earlier ceiling of 225 is ‘no longer possible, and the UK will move to an overall nuclear weapon stockpile of no more than 260 warheads.’ The Integrated Review also stated, however, that the UK government intended to extend its ‘long-standing policy of deliberate ambiguity and no longer give public figures for our operational stockpile, deployed warhead or deployed missile numbers.’[1] The most recent Strategic Defence Review and National Security Strategy, published by the UK government in 2025, did not recommend a warhead ceiling.[2]
The announcement in 2021 signalled the end of a series of post-Cold War reductions in the overall UK nuclear weapon stockpile as follows:
—In 1988, the UK government announced its intention to limit the total number of warheads for the new Trident system to 512 and that it would deploy no more than 128 warheads per submarine.[3] This was reduced again in 1995 to a total of 300 warheads with a maximum of 96 per submarine, and later to a maximum of 60 warheads per submarine.[4]
—In 1998, the government announced a reduction in the number of operationally available Trident warheads to no more than 200.[5]
—In 2006 the government announced that it would reduce the number of operationally available warheads by 20% to 160.[6]
—In the 2010 UK Strategic Defence and Security Review, the UK government announced its intention to reduce its overall nuclear warhead stockpile ceiling from not more than 225 to not more than 180 by the mid 2020s, and to reduce its operationally available warheads from fewer than 160 to no more than 120.[7] In 2015, the statement from 2010 was repeated in the government’s Strategic Defence and Security Review.[8]
Last updated: 22 April 2026 18:43
The explosive yields of UK warheads are classified([1]. However, the House of Commons Library stated in a report in 2016 that the UK Holbrook warhead ‘is believed to be closely related to the American W76 warhead, a thermonuclear warhead in the 80-100 kiloton range.'[2]
This is because the UK Holbrook warhead is understood to be an Anglicised version of the US W76-1 warhead. For example, Franklin Miller KGB, Special Advisor to President George W Bush and Senior Director for Defense Policy and Arms Control, described the UK warhead as ‘their W76 variant’.[3]
The US deploys the W76-1 warhead on its Trident II (D5) submarine-launched ballistic missiles (SLBMs). The United Kingdom also deploys its Holbrook warhead on Trident II (D5) SLBMs under a lease arrangement for 58 missile bodies drawn from a common pool in the US.[4] The UK warhead must therefore match the size, mass, centre of gravity and other characteristic requirements for the US-supplied warhead re-entry body designed to operate with the Trident missile.
The Holbrook warhead can also be detonated at a lower yield, described by the government in the 1990s as a ‘sub-strategic’ option,[5] using a variant of the warhead with no secondary and detonating only the primary stage only. The government confirmed in 1997 that ‘The UK has some flexibility in the choice of yield for the warheads on its Trident missiles’.[6] The US deployed a reduced yield variant of its W76 warhead (the W76-[2] in 2019 by configuring a small number of existing warheads for primary-only detonation.[7] It is not clear if a low-yield variant exists within the current UK stockpile.
Last updated: 22 April 2026 18:43