Just over three years after it was negotiated, the Treaty on the Prohibition of Nuclear Weapons has been ratified by its 50th State Party. This means it can now enter into force on 22 January 2021.

None of the nine nuclear weapon states have signed or ratified the treaty, including the UK.

This Insight examines the main provisions of the treaty and what it means for the UK.

What the treaty does

The Treaty on the Prohibition of Nuclear Weapons was adopted on 7 July 2017. It’s the first multilateral, legally-binding, instrument for nuclear disarmament to have been negotiated in 20 years. It needs to be ratified by 50 State Parties before coming into force (90 days after the fiftieth ratification).

The treaty prohibits State Parties from developing, testing, producing, manufacturing, acquiring, possessing, stockpiling, transferring or receiving control over nuclear weapons or other nuclear explosive devices. It also prohibits them from using, or threatening to use, such weapons.

State Parties are also required to prohibit and prevent the stationing, installation, or deployment of nuclear weapons on their territory or any other place under its jurisdiction or control.

The treaty requires State Parties to have, at a minimum, a Comprehensive Safeguards Agreement with the International Atomic Energy Agency.

For the first time, it also requires State Parties to provide victim assistance and environmental remediation to those affected by nuclear weapons use and testing.

Its long-awaited entry into force

In July 2017, 122 countries voted in favour of the treaty. It opened for signatures from any UN member state, regardless of their participation in the treaty conference, on 20 September that year.

Honduras was the 50th state to ratify the treaty on 24 October 2020. It will now come into force on 22 January 2021 and take full legal effect for those countries which have signed and ratified it by that date. A further 34 countries have signed but not yet ratified the treaty. The treaty also remains open to accession by any state after it’s entered force.

For any state that ratifies or accedes to the treaty after it enters into force, its provisions will take full legal effect 90 days later.

None of the nuclear weapon states, or those who fall under the US and NATO nuclear umbrella, have signed or ratified the treaty.

Who are the nuclear weapon states?

There are nine countries in the world that possess approximately 13,400 operational and non-operational nuclear weapons between them.

More than 90% belong to Russia and the United States. Of the remaining nuclear countries, only the UK (approximately 195 warheads) and France have reduced the size of their nuclear arsenals since the end of the Cold War. China, India, Pakistan and North Korea have been actively expanding their nuclear stockpiles. All nine countries continue to modernise their nuclear capabilities.

A chart shows the estimated number of stockpiled operational warheads over time (excluding United States and Russia). Only the UK and France have reduced the size of their nuclear arsenals.

Is the UK bound to anything?

The UK did not participate in negotiations in 2017 and has not signed and ratified the treaty. Therefore, the UK is not legally bound its provisions.

The Government has also made clear that the UK will not “accept any argument that this treaty can constitute a development of customary international law binding on the UK or on other non-parties.”

Successive governments have consistently held the view that the best way to achieve the goal of global nuclear disarmament is through gradual multilateral disarmament, negotiated using a step-by-step approach and within existing international frameworks, such as the Nuclear Non-Proliferation Treaty (NPT).

Article VI, NPT

Each of the Parties to the Treaty undertakes to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament, and on a treaty on general and complete disarmament under strict and effective international control.

What can the treaty therefore hope to achieve?

Without the involvement of the nine nuclear weapon states, there is a concern the treaty risks becoming symbolic and of little practical use in the pursuit of disarmament.

However, advocates such as the International Campaign to Abolish Nuclear Weapons argue it will have a moral effect and pressure the nuclear countries, and their allies, to alter their behaviour and help shape the international norm against nuclear weapons. Many have expressed hope that it will provide a stimulus for further action on nuclear disarmament.

The Spokesman for the UN Secretary General António Guterres recently hailed the treaty’s entry into force and said it represented: “a meaningful commitment towards the total elimination of nuclear weapons, which remains the highest disarmament priority of the United Nations.”

Further reading

A Treaty on the Prohibition of Nuclear Weapons, House of Commons Library.

Nuclear Weapons – Country Comparisons, House of Commons Library.


About the author: Claire Mills is a researcher at the House of Commons Library, specialising in defence.

Image: HMS Vengeance returning to HMNB Clyde by Ministry of Defence, under Open Government License.