Fact Sheet

Nuclear Disarmament United Kingdom

Part of Nuclear Disarmament Resource Collection

Nuclear Disarmament United Kingdom

Arsenal and Missile Types

NPT Nuclear Weapon State

Arsenal Size

  • Total warheads: Approximately 225
  • Operationally available warheads: Approximately 120
  • The government announced in 2021 intention to increase stockpile ceiling to up to 260 warheads (increased from its 2010 commitment to a ceiling of 180 warheads)1

Weapon System

  • The UK is the only nuclear weapon state (NWS) with a single weapon system (the Trident II D5 SLBM) and has the smallest nuclear arsenal of the five official NWS.
  • Four Vanguard-class nuclear-powered ballistic missile submarines (SSBNs), armed with Trident II D5 SLBMs. The United Kingdom’s policy of Continuous At Sea Deterrence (CASD) requires that one Vanguard-class submarine be on patrol at all times.
  • New Dreadnought-class SSBNs planned to replace the Vanguard-class fleet starting in the early 2030s.2

Capabilities and Developments

Military Fissile Material Stockpile

  • Weapon-Grade Plutonium: 3.2 metric tons
  • Military Highly Enriched Uranium (HEU): 22 metric tons3

Commitments and Policies

Disarmament and Commitments to Reduce Arsenal Size

  • Legal obligation to pursue global disarmament under Article VI of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT).
  • Although the UK government has stated its plan to reduce the size of its nuclear stockpile to no more than 180 by the mid-2020s, the stockpile remains constant.

Future Commitment

  • The UK is a member of the FMCT (Fissile Material Cut-Off Treaty) Friends group and supports the early start of the treaty negotiation4

Nuclear Weapons Policies

  • The UK maintains “minimum, credible, independent” nuclear deterrence to deter threats against the country and NATO.
  • The UK joined all other nuclear weapons possessing states in boycotting the 2017 negotiations on the Treaty on the Prohibition of Nuclear Weapons (TPNW) at the UN General Assembly. The UK has no plans to join the (TPNW).5

Nuclear Testing

  • Observed nuclear testing moratorium since 1991
  • Signed and ratified the Comprehensive Nuclear Test Ban Treaty (CTBT).6

Use of Nuclear Weapons

  • The UK would consider the use of nuclear weapons “only in extreme circumstances of self-defence, including the defence of our NATO allies” but remains “deliberately ambiguous about precisely when, how, and at what scale” it would use them.7
  • “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. This assurance does not apply to any state in material breach of those non-proliferation obligations.”8
  • The UK has ratified the protocols of Negative Security Assurances in four of the five Nuclear-Weapon-Free Zone (NWFZ) treaties: the treaty of Tlatelolco,  Rarotonga,  Pelindaba, and Semipalatinsk.  It has not signed or ratified the protocol of the SE Asian NWFZ (Bangkok Treaty).9

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Glossary

Treaty on the Non-Proliferation of Nuclear Weapons (NPT)
The NPT: Signed in 1968, the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) is the most widely adhered-to international security agreement. The “three pillars” of the NPT are nuclear disarmament, nonproliferation, and peaceful uses of nuclear energy. Article VI of the NPT commits states possessing nuclear weapons to negotiate in good faith toward halting the arms race and the complete elimination of nuclear weapons. The Treaty stipulates that non-nuclear-weapon states will not seek to acquire nuclear weapons, and will accept International Atomic Energy Agency safeguards on their nuclear activities, while nuclear weapon states commit not to transfer nuclear weapons to other states. All states have a right to the peaceful use of nuclear energy, and should assist one another in its development. The NPT provides for conferences of member states to review treaty implementation at five-year intervals. Initially of a 25-year duration, the NPT was extended indefinitely in 1995. For additional information, see the NPT.
Ballistic missile
A delivery vehicle powered by a liquid or solid fueled rocket that primarily travels in a ballistic (free-fall) trajectory.  The flight of a ballistic missile includes three phases: 1) boost phase, where the rocket generates thrust to launch the missile into flight; 2) midcourse phase, where the missile coasts in an arc under the influence of gravity; and 3) terminal phase, in which the missile descends towards its target.  Ballistic missiles can be characterized by three key parameters - range, payload, and Circular Error Probable (CEP), or targeting precision.  Ballistic missiles are primarily intended for use against ground targets.
SSBN
Ship, Submersible, Ballistic, Nuclear: A hull classification for a submarine capable of launching a ballistic missile. The "N", or nuclear, refers to the ship's propulsion system. SSBN's are generally reserved for strategic vessels, as most submarine launched ballistic missiles carry nuclear payloads. A non-strategic vessel carries the designation SSN, or attack submarine.
Plutonium (Pu)
Plutonium (Pu): A transuranic element with atomic number 94, produced when uranium is irradiated in a reactor. It is used primarily in nuclear weapons and, along with uranium, in mixed-oxide (MOX) fuel. Plutonium-239, a fissile isotope, is the most suitable isotope for use in nuclear weapons.
Highly enriched uranium (HEU)
Highly enriched uranium (HEU): Refers to uranium with a concentration of more than 20% of the isotope U-235. Achieved via the process of enrichment. See entry for enriched uranium.
Disarmament
Though there is no agreed-upon legal definition of what disarmament entails within the context of international agreements, a general definition is the process of reducing the quantity and/or capabilities of military weapons and/or military forces.
Treaty on the Non-Proliferation of Nuclear Weapons (NPT)
The NPT: Signed in 1968, the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) is the most widely adhered-to international security agreement. The “three pillars” of the NPT are nuclear disarmament, nonproliferation, and peaceful uses of nuclear energy. Article VI of the NPT commits states possessing nuclear weapons to negotiate in good faith toward halting the arms race and the complete elimination of nuclear weapons. The Treaty stipulates that non-nuclear-weapon states will not seek to acquire nuclear weapons, and will accept International Atomic Energy Agency safeguards on their nuclear activities, while nuclear weapon states commit not to transfer nuclear weapons to other states. All states have a right to the peaceful use of nuclear energy, and should assist one another in its development. The NPT provides for conferences of member states to review treaty implementation at five-year intervals. Initially of a 25-year duration, the NPT was extended indefinitely in 1995. For additional information, see the NPT.
United Nations General Assembly
The UN General Assembly is the largest body of the United Nations. It includes all member states, but its resolutions are not legally binding. It is responsible for much of the work of the United Nations, including controlling finances, passing resolutions, and electing non-permanent members of the Security Council. It has two subsidiary bodies dealing particularly with security and disarmament: the UN General Assembly Committee on Disarmament and International Security (First Committee); and the UN Disarmament Commission. For additional information, see the UNGA.
Ratification
Ratification: The implementation of the formal process established by a country to legally bind its government to a treaty, such as approval by a parliament. In the United States, treaty ratification requires approval by the president after he or she has received the advice and consent of two-thirds of the Senate. Following ratification, a country submits the requisite legal instrument to the treaty’s depository governments Procedures to ratify a treaty follow its signature.

See entries for Entry into force and Signature.
Comprehensive Nuclear-Test-Ban Treaty (CTBT)
The CTBT: Opened for signature in 1996 at the UN General Assembly, the CTBT prohibits all nuclear testing if it enters into force. The treaty establishes the Comprehensive Test Ban Treaty Organization (CTBTO) to ensure the implementation of its provisions and verify compliance through a global monitoring system upon entry into force. Pending the treaty’s entry into force, the Preparatory Commission of the CTBTO is charged with establishing the International Monitoring System (IMS) and promoting treaty ratifications. CTBT entry into force is contingent on ratification by 44 Annex II states. For additional information, see the CTBT.
Ratification
Ratification: The implementation of the formal process established by a country to legally bind its government to a treaty, such as approval by a parliament. In the United States, treaty ratification requires approval by the president after he or she has received the advice and consent of two-thirds of the Senate. Following ratification, a country submits the requisite legal instrument to the treaty’s depository governments Procedures to ratify a treaty follow its signature.

See entries for Entry into force and Signature.
Nuclear-Weapon-Free Zone (NWFZ)
NWFZ: A geographical area in which nuclear weapons may not legally be built, possessed, transferred, deployed, or tested.
Treaty of Tlatelolco
The Treaty of Tlatelolco: This treaty, opened for signature in February 1967, created a nuclear-weapon-free zone in Latin America and the Caribbean. The Treaty of Tlatelolco was the first international agreement that aimed to exclude nuclear weapons from an inhabited region of the globe. The member states accept the application of International Atomic Energy Agency safeguards on all their nuclear activities. The treaty also establishes a regional organization, the Agency for the Prohibition of Nuclear Weapons in Latin America (OPANAL), to supervise treaty implementation and ensure compliance with its provisions. For additional information, see the LANWFZ.
Treaty of Rarotonga
Treaty of Rarotonga: The Treaty on the South Pacific Nuclear-Weapon-Free Zone (SPNWFZ) prohibits the testing, manufacturing, acquiring, and stationing of nuclear explosive devices on any member's territory. The treaty also prohibits the dumping of radioactive wastes into the sea. In addition, the treaty required all parties to apply International Atomic Energy Agency safeguards to all their peaceful nuclear activities. For additional information, see the SPNWFZ.
Treaty of Pelindaba
Treaty of Pelindaba: The Treaty on the African Nuclear-Weapon-Free-Zone was opened for signature in Cairo in April 1996. The treaty prohibits the research, development, manufacturing, stockpiling, acquisition, testing, possession, control, and stationing of nuclear explosive devices on any member’s territory. The treaty also prohibits the dumping of radioactive waste originating from outside the continent within the region. In addition, the treaty requires parties to apply International Atomic Energy Agency safeguards to all their peaceful nuclear activities. The treaty also provides for the establishment of the African Commission on Nuclear Energy (AFCONE), which supervises treaty implementation and ensures compliance with its provisions. For additional information, see the ANWFZ.
Southeast Asian Nuclear-Weapon-Free-Zone (SEANWFZ)
The Treaty on the Southeast Asian Nuclear-Weapon-Free-Zone (SEANWFZ) prohibits the development, manufacture, acquisition, or testing of nuclear weapons anywhere within the region. It also prohibits the transport of nuclear weapons through the region, as well as the dumping at sea, discharging into the atmosphere, or burying on land of any radioactive material or waste. In addition, the treaty requires all parties to apply International Atomic Energy Agency safeguards to all their peaceful nuclear activities. For additional information, see the SEANWFZ.
Treaty of Bangkok
Treaty of Bangkok: The Treaty on the Southeast Asian Nuclear-Weapon-Free-Zone prohibits the development, manufacture, acquisition, or testing of nuclear weapons anywhere within the region. It also prohibits the transport of nuclear weapons through the region, as well as the dumping at sea, discharging into the atmosphere, or burying on land of any radioactive material or waste. In addition, the treaty requires all parties to apply International Atomic Energy Agency safeguards to all their peaceful nuclear activities. For additional information, see the SEANWFZ.

Sources

  1. Hans M. Kristensen and Matt Korda, “6. World Nuclear Forces,” in SIPRI Yearbook 2025: Armaments, Disarmament and International Security, 56th ed., SIPRI Yearbook Series (Oxford, New York: Oxford University Press, 2025), 177–213, www.sipri.org.
  2. Hans M. Kristensen et al., “United Kingdom Nuclear Weapons, 2024,” Bulletin of the Atomic Scientists 80, no. 6 (November 1, 2024): 394–407, https://doi.org/10.1080/00963402.2024.2420550.
  3. “Fissile Material Stocks,” International Panel on Fissile Materials, April 28, 2025, https://fissilematerials.org.
  4. Daryl Kimball, “Fissile Material Cut-off Treaty (FMCT) at a Glance,” Arms Control Association, November 2024, www.armscontrol.org.
  5. “United Kingdom,” ICAN, accessed July 21, 2025, www.icanw.org.
  6. Daryl Kimball, “Nuclear Testing and Comprehensive Test Ban Treaty (CTBT) Timeline,” Arms Control Association, April 2025, www.armscontrol.org.
  7. “The UK’s Nuclear Deterrent: What You Need to Know,” March 28, 2024, www.gov.uk.
  8. Conference on Disarmament: Minister Cleverly’s Address on the UK Integrated Review,” March 26, 2021, www.gov.uk.
  9. Davenport, Kelsey, “Nuclear-Weapon-Free Zones (NWFZ) at a Glance,” Arms Control Association, March 2022, www.armscontrol.org.
  1. Joanne Adamson, “Statement: Cluster II – Non-Proliferation,” 2012 Preparatory Committee for the Nuclear Non-Proliferation Treaty, May 7, 2012, www.reachingcriticalwill.org.
  2. Joanne Adamson, “Statement on Fissile Material Cutoff Treaty,” Council on Disarmament, March 12, 2013, www.reachingcriticalwill.org.
  3. Shubhra Chaturvedi, “Southeast Asian Nuclear Weapon Free Zone Treaty: What’s Holding It Up?” International Peace and Conflict Studies, July 31, 2012, www.ipcs.org.
  4. CTBTO Preparatory Commission, “Status of Signature and Ratification,” www.ctbto.org.
  5. “Nuclear Weapon Free Zone (NWFZ) Clearinghouse,” James Martin Center for Nonproliferation Studies, www.nonproliferation.org.
  6. “Inventory of International Nonproliferation Organizations & Regimes,” James Martin Center for Nonproliferation Studies, www.nonproliferation.org.
  7. Hans M. Kristensen and Matt Korda, “United Kingdom nuclear weapons, 2021,” Bulletin of the Atomic Scientists 77, No. 3 (2021), pp. 153-158.
  8. Hans M. Kristensen, Matt Korda, Eliana Johns, Mackenzie Knight, and Kate Kohn, “Status of World Nuclear Forces,” Federation of American Scientists, March 29, 2024, www.fas.org.
  9. “Main Committee I Statement,” Report by Mr. Guy Pollard, Deputy Permanent Representative of the United Kingdom to the Conference on Disarmament, 2015 Review Conference of the Treaty on Non-Proliferation of Nuclear Weapons, April 27-May 22, 2015.
  10. “United Kingdom,” International Campaign to Abolish Nuclear Weapons, www.icanw.org.
  11. “The UK’s Nuclear Deterrent: What You Need to Know,” Defense Nuclear Organisation, March 28, 2024, www.gov.uk.
  12. United Nations, “Treaty banning nuclear weapon tests in the atmosphere, in outer space and under water,” https://treaties.un.org.
  13. “Countries: United Kingdom,” International Panel on Fissile Materials, April 13, 2024, https://fissilematerials.org.
  14. “Fissile material stocks,” International Panel on Fissile Materials, April 13, 2024, https://fissilematerials.org.

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