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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 (C3) system, 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
When asked in parliament in 2025 “if artificial intelligence has been used to support (a) routine operations and (b) policy in relation to nuclear capability”, the government 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, the House of Lords ‘Artificial Intelligence in Weapon Systems Committee’ published its report.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
The UK deploys a single nuclear delivery system - the Trident II (D5) SLBM. The UK originally purchased title to 65 Trident SLBMs from the US under the 1963 Polaris Sales Agreement amended for procurement of Trident in 1982 1. This was reduced to 58 in 1998 (2). The missiles are designed, produced, stored, and maintained in the US when they are not deployed on the UK’s fleet of four Vanguard-class SSBNs. The UK pays an annual contribution to the continued maintenance of the missile stock (3).
Some UK missiles have been used in live test fires. 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. The UK had test fired eleven missiles as of January 2017 (4).
In 2010 the government’s Strategic Defence and Security Review stated it was reducing “the number of operational missiles 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). The change was completed in January 2015 (7).
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) The 2025 Strategic Defence Review and the 2025 National Security Strategy provided no details on missile numbers or deployments.
The government stated in 2021 that the UK had sufficient Trident II D5 missiles for its needs” (9). The UK only deploys nuclear warheads on its Trident missiles.
The UK has one nuclear weapons delivery system comprising US Trident II (D5) SLBMs deployed across a fleet of four Vanguard-class UK 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.
The UK has publicly stated 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 UK does not deploy any other types of nuclear weapons or any other nuclear delivery vehicles. The UK's last air-launched nuclear weapons (WE177 gravity bombs) were withdrawn in 1997(4).
The UK does not operate any fissile material production or reprocessing facilities for nuclear weapons purposes and “ceased the production of fissile material for explosive purposes” in April 1995. 1
Production of HEU for defence programmes at the UK’s Capenhurst Plant ended in 1962. Since then the UK 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 plant was modified to produce Low Enriched Uranium (LEU) for civil nuclear power reactors until it ceased operations in 1982.
The UK has operated three reprocessing facilities at its Sellafield nuclear site: the First Generation Reprocessing Plant (B204) from 1952 to 1964 to extract plutonium from spent nuclear fuel for the UK’s 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. 2
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, Calder Hall reactors were brought under Euratom safeguards and made liable to inspection under the terms of the safeguards agreement between the UK, 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 be conducted under Euratom safeguards and made liable to inspection by IAEA. Chapelcross ceased operations in 2004.
The UK partially discloses its total holdings of low-enriched uranium, highly-enriched uranium, and plutonium. The UK “ceased the production of fissile material for explosive purposes” in April 1995.1 In 2000 the UK published a historical accounting of its plutonium production for defence purposes up to 1999.1 In 2006 the UK published a historical accounting of its production of Highly Enriched Uranium for defence purposes up to 2002.2 It has not updated the figures in these reports. The UK also provides the IAEA a statement of its annual figures for holdings of civil high-enriched uranium and civil depleted, natural and low enriched uranium in its civil nuclear fuel cycle.3
The UK submits regular reporting of civil fissile material holdings to the IAEA, typically monthly.4 Separately from day-to-day safeguards, the UK also provides to the IAEA a statement of its annual figures for holdings of civil high enriched uranium and civil depleted, natural and low enriched uranium in its civil nuclear fuel cycle under INFCIRC/549.3 This is a set of voluntary transparency guidelines established in 1998 under which participating states publish annual, public figures for their civil unirradiated plutonium (plus an estimate for plutonium in spent fuel), along with short policy statements. Some states, including the UK, have chosen to add civil HEU figures for the purposes of transparency.
The UK reiterated in 2010 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 held outside the international safeguards regime. It is subject to a strict internal materials accountancy regime.5
Yes, the UK government does disclose its high-level plans and strategic rationale for the modernisation of its nuclear arsenal, though it has simultaneously increased ambiguity around its operational details.
The UK's strategic rationale for modernising its deterrent is a direct response to a perceived ‘deteriorating security environment’. The 2023 Integrated Review Refresh explicitly states 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
Plans for modernising nuclear weapon systems and the nuclear weapons complex are public and well-established. The UK has publicly stated it is:
Building four new Dreadnought-class SSBNs at BAE Systems Barrow shipyard to replace the current fleet of Vanguard-class ballistic missile submarines, with the first of class - HMS Dreadnought - expected to enter service in the early 2030s.
Planning to deploy the US designed and built Trident II D5LE SLBM as deployed on the Vanguard-class to be replaced by the D5LE2 from the 2040s.2
Purchasing 12 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
Undergoing a massive, multi-billion-pound infrastructure modernisation as part of the Nuclear Warhead Capability Sustainment Programme to support the design and production of a new warhead. This includes the Project MENSA warhead assembly/disassembly facility at the 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.
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.
Exploring options to re-establish a nuclear fuel cycle for reactor fuel for defence purposes.4
On fissile material production: The UK has not produced fissile material (highly enriched uranium or plutonium) for weapons since 1995 and maintains a moratorium on this. 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.
The UK 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
In 2015 the UK stated 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 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
The UK partially discloses its policy regarding when the employment of nuclear weapons would be considered. The UK does not set out specific conditions determining when it would consider using nuclear weapons because of the strategic importance of maintaining ‘deliberate ambiguity’. However, it does provide some parameters in terms of using nuclear weapons only in extreme circumstances of self-defence, the definition of which would be determined by the UK.
For example, the UK stated in 2021 that it “would consider using our nuclear weapons only in extreme circumstances of self-defence, including the defence of our NATO Allies” and that “While our resolve and capability to do so if necessary is beyond doubt, we will remain deliberately ambiguous about precisely when, how and at what scale we would contemplate the use of nuclear weapons”.1
The use of “extreme circumstances of self-defence” reflects wording the 1996 Advisory Opinion of the International Court of Justice on the Legality of the Use or Threat of Use of Nuclear Weapons. The ICJ concluded that it “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”.
In 2006 the UK government stated that “In 1996 the International Court of Justice delivered an Advisory Opinion which confirmed that the use, or threat of use, of nuclear weapons is subject to the laws of armed conflict, and rejected the argument that such use would necessarily be unlawful. The threshold for the legitimate use of nuclear weapons is clearly a high one. We would only consider using nuclear weapons in self-defence (including the defence of our NATO allies), and even then only in extreme circumstances. The legality of any such use would depend upon the circumstances and the application of the general rules of international law, including those regulating the use of force and the conduct of hostilities”. 3
The UK has also eschewed language of ‘sub-strategic’ use of its Trident nuclear weapons system. It has stated 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 and that “The UK does not categorise nuclear weapon capabilities as either strategic or sub-strategic/tactical. The UK and NATO have said that any employment of nuclear weapons against NATO would fundamentally alter the nature of a conflict. The UK’s nuclear weapons are a tool aiming 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
The UK does not have a ‘no first use’ pledge. This is because “UK and NATO nuclear doctrine are consistent. NATO’s long-standing policy is neither to rule in nor rule out first use of nuclear weapons”.6 Specially: “The UK does not have a policy of no first use because—this goes to the heart of much of what we are discussing—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
The UK participates in multilateral transparency arrangements, mainly through the Hague Code of Conduct against Ballistic Missile Proliferation (HCOC) that commits 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 that is shared with all other HCoC subscribing states through a dedicated online platform.
The UK provides post-launch notification to the UN 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 SSBN patrols or 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 exercise, including exercise involving nuclear assets.
No. The UK 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.
The UK 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 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 we would contemplate the use of nuclear weapons.1
The UK government does not disclose the total number of nuclear warheads in its stockpile. Instead, it has regularly disclosed a warhead ceiling. The most recent disclosure was in Conservative Johnson government’s 2021 Integrated Review of Security, Defence, Development and Foreign Policy. This stated that the government was increasing the overall nuclear weapon stockpile to no more than 260 warheads 1. The most recent Strategic Defence Review and National Security Strategy published by the Labour Starmer government in 2025 did not declare a warhead ceiling (2).
The announcement in 2021 signalled the end of a post-Cold War series of reductions in the overall nuclear weapon stockpile as follows:
- In 1988 Conservative Thatcher 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 a maximum of 96 per submarine and later to a maximum of 60 warheads per submarine (4).
- In 1998 the Labour Blair government announced a reduction in the number of operationally available Trident warheads to no more than 200 (5).
- In 2006 the Labour government announced that it would reduce the number of operationally available warheads by 20% to 160 (6).
- In 2010 the Conservative-Liberal Democrat Coalition government’s 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 reduce its operationally available warheads from fewer than 160 to no more than 120 in its 2010 Strategic Defence and Security Review. (7).
- In 2015 the 2010 statement was repeated in the Conservative Cameron government’s Strategic Defence and Security Review. (8)
The explosive yields of UK warheads are classified 1. However, the UK Holbrook warhead is understood to have a yield of 80-100 kilotons 2. The House of Commons Library stated in a report in 2016 that the UK warhead “is believed to be closely related to the American W76 warhead, a thermonuclear warhead in the 80-100 kiloton range”.(3)
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”. (4) The W76 warhead is widely understood to have an explosive yield of 80-100 kt. However, this figure has not been declared in official US documents.
This is because the US deploys the W76-1 warhead on its Trident II (D5) SLBMs. The UK 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 (5). The UK warhead therefore has to match the size, mass, centre of gravity and other characteristic requirements for the US-supplied warhead re-entry body designed to operate with Trident missile.
The Holbrook warhead can also be detonated at a lower yield, described in the 1990s as a ‘sub-strategic’ option (6) by configuring a warhead to detonate the primary stage only and/or adjusting the height of the detonation over the target (7). The government confirmed in 1997 that “The UK has some flexibility in the choice of yield for the warheads on its Trident missiles” (8). 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 (9).