Her Majesty’s Government – 30th April 2021 – Integrated Review of Security, Defence, Development and Foreign Policy 2021: Nuclear Deterrent.

Her Majesty’s Government – 30 April 2021

Integrated Review of Security, Defence, Development and Foreign Policy 2021: nuclear deterrent


The 2021 Integrated Review set out the government’s vision for the future. This page outlines what is says about the UK’s nuclear deterrent.

The nuclear deterrent

The UK’s independent nuclear deterrent has existed for over 60 years to deter the most extreme threats to our national security and way of life, helping to guarantee our security and that of our Allies. We have previously identified risks to the UK from major nuclear armed states, emerging nuclear states, and state-sponsored nuclear terrorism. Those risks have not gone away. Some states are now significantly increasing and diversifying their nuclear arsenals. They are investing in novel nuclear technologies and developing new ‘warfighting’ nuclear systems which they are integrating into their military strategies and doctrines and into their political rhetoric to seek to coerce others. The increase in global competition, challenges to the international order, and proliferation of potentially disruptive technologies all pose a threat to strategic stability. The UK must ensure potential adversaries can never use their capabilities to threaten us or our NATO Allies. Nor can we allow them to constrain our decision-making in a crisis or to sponsor nuclear terrorism.

The UK’s minimum, assured, credible nuclear deterrent

The fundamental purpose of our nuclear weapons is to preserve peace, prevent coercion and deter aggression. A minimum, credible, independent nuclear deterrent, assigned to the defence of NATO, remains essential in order to guarantee our security and that of our Allies. In 2010 the Government stated an intent to reduce our overall nuclear warhead stockpile ceiling from not more than 225 to not more than 180 by the mid-2020s.

However, in recognition of the evolving security environment, including the developing range of technological and doctrinal threats, this is no longer possible, and the UK will move to an overall nuclear weapon stockpile of no more than 260 warheads.

To ensure that our deterrent is not vulnerable to pre-emptive action by potential adversaries, we will maintain our four submarines so that at least one will always be on a Continuous At Sea Deterrent patrol. Our submarines on patrol are at several days’ notice to fire and, since 1994, we do not target our missiles at any state. We remain committed to maintaining the minimum destructive power needed to guarantee that the UK’s nuclear deterrent remains credible and effective against the full range of state nuclear threats from any direction.

We will continue to keep our nuclear posture under constant review in light of the international security environment and the actions of potential adversaries. We will maintain the capability required to impose costs on an adversary that would far outweigh the benefits they could hope to achieve should they threaten our, or our Allies’, security.

UK nuclear weapons policy

The UK’s nuclear weapons are operationally independent and only the Prime Minister can authorise their use. This ensures that political control is maintained at all times. We would consider using our nuclear weapons only in extreme circumstances of self-defence, including the defence of our NATO Allies.

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. Given the changing security and technological environment, we will extend this long-standing policy of deliberate ambiguity and no longer give public figures for our operational stockpile, deployed warhead or deployed missile numbers. This ambiguity complicates the calculations of potential aggressors, reduces the risk of deliberate nuclear use by those seeking a first-strike advantage, and contributes to strategic stability.

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.

Working with NATO, the US and France

NATO recognises that any employment of nuclear weapons against NATO would fundamentally alter the nature of a conflict. Therefore, as long as nuclear weapons exist, NATO will remain a nuclear alliance. Since 1962, the UK has declared our nuclear capability to the defence of the Alliance. We will continue to do so, safeguarding European and Euro-Atlantic security. We will work with Allies to ensure that NATO’s nuclear deterrent capabilities remain safe, secure and effective, adapt to emerging challenges including the growing and diversifying nuclear threats that the Alliance may face, and contribute to the indivisible security of the Alliance.

Nuclear cooperation remains an important element of the relationship between the United States and the United Kingdom, enhancing transatlantic security. We will continue to work closely with the United States on nuclear matters, including nuclear deterrence policy.

The 1958 Mutual Defense Agreement (MDA) has been central to our shared nuclear security goals and we are committed to its renewal in 2024.

Since 1995, France and the United Kingdom, Europe’s only nuclear powers, have stated that they can imagine no circumstances under which a threat to the vital interests of one would not constitute a threat to the vital interests of the other. We will continue our daily and unprecedented cooperation on nuclear issues, including our collaboration under the 2010 Teutates Treaty.

Our future capability

Our independent nuclear deterrent is relevant not only for today but will also remain relevant for the immediate future. It is for these reasons that we have committed to a once-in-two-generations programme to modernise our nuclear forces. This investment in the future security of both the UK and our Allies demonstrates that the UK’s nuclear commitment remains undiminished.

Parliament has voted to renew our nuclear deterrent and replace the Vanguard Class submarines with four new Dreadnought Class submarines. The programme remains within budget and on track for the First of Class to enter service in the early 2030s.

To ensure we maintain an effective deterrent throughout the commission of the Dreadnought Class, we will replace our existing nuclear warhead. We will work with the Atomic Weapons Establishment to build the highly skilled teams, facilities and capabilities needed to deliver this, while also sustaining the current warhead until it is withdrawn from service. We will continue to work closely with the United States to ensure our warhead remains compatible with the Trident Strategic Weapon System, our cooperation underpinned by both the MDA and the 1963 Polaris Sales Agreement.

Delivery of the modernisation of the deterrent will be subject to the government’s major programme approvals and oversight. We will continue to provide updates through an annual report to Parliament. We will work collaboratively across the defence and civil nuclear sectors to optimise the Defence Nuclear Enterprise for the future. This will ensure that the UK has a minimum, credible, independent nuclear deterrent for as long as is necessary.

Arms control, disarmament and non-proliferation: our commitment to international treaties

We remain committed to the long-term goal of a world without nuclear weapons. We continue to work for the preservation and strengthening of effective arms control, disarmament and non-proliferation measures, taking into account the prevailing security environment. We are strongly committed to full implementation of the NPT in all its aspects, including nuclear disarmament, non-proliferation, and the peaceful uses of nuclear energy; there is no credible alternative route to nuclear disarmament. The UK has taken a consistent and leading approach to nuclear disarmament. The UK possesses the smallest stockpile of any of the nuclear weapon states recognised by the NPT. We are alone amongst those states in only operating a single nuclear weapon system. We will continue to press for key steps towards multilateral disarmament, including the entry into force of the Comprehensive Nuclear Test Ban Treaty and successful negotiations on a Fissile Material Cut-Off Treaty in the Conference on Disarmament. We will continue to take a leading international role on nuclear disarmament verification; this is an essential step for nuclear disarmament under strict and effective international control.

The UK will continue to work internationally to reduce the risk of nuclear conflict and enhance mutual trust and security. We will champion strategic risk reduction and seek to create dialogue among states possessing nuclear weapons, and between states possessing nuclear weapons and non-nuclear weapon states, to increase understanding and reduce the risk of misinterpretation and miscalculation. The UK takes its responsibilities as a nuclear weapon state seriously and will continue to encourage other states to do likewise.