26 April 2021
Dear Ms Zelter, Mr Larkin, Mr Morgan and Mr Mackenzie,
Thank you for your email to the Secretary of State for Defence, dated 25 March 2021, regarding nuclear aspects of the Government’s Integrated Review of Security, Defence, Development and Foreign Policy, published on 16 March 2021. As the Defence Nuclear Organisation is the part of the Ministry of Defence responsible for matters relating to the United Kingdom’s (UK’s) nuclear deterrent, we have been asked to respond on his behalf.
The UK’s nuclear deterrent exists to deter the most extreme threats to our national security and way of life, which cannot be deterred by other means. It will remain essential for as long as the global security situation demands.
The UK is committed to maintaining the minimum destructive power needed to guarantee the nuclear deterrent remains credible and effective against the full range of state nuclear threats from any direction. This is fully compliant and compatible with our international legal obligations, including those under Article VI of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). As announced in the Integrated Review, in recognition of the evolving security environment, including the developing range of technological and doctrinal threats, the UK will move to an overall nuclear weapon stockpile of no more than 260 warheads. We regret that the security environment has necessitated this change from the previous ceiling of no more than 225 and prevented us from meeting our previously stated intention of reducing to no more than 180 by the mid-2020s. Despite this, we possess the smallest stockpile of the five nuclear weapon states recognised under the NPT.
We do have a close and longstanding relationship with the United States (US) on all nuclear issues and we continue to co-operate with France. We can assure you that our activities under the 1958 Mutual Defence Agreement, 1963 Polaris Sales Agreement (as amended for Trident) and 2010 Teutates Treaty are fully compliant with our international legal obligations. Article I of the NPT prohibits the transfer to any recipient whatsoever nuclear weapons or other nuclear explosive devices; no such transfer takes place under the terms of our co-operation with the US and France.
Our negative security assurances have not changed. The UK will not use, or threaten to use, nuclear weapons against any non-nuclear weapon state party to the NPT. This assurance does not apply to any state in material breach of those non-proliferation obligations. The Integrated Review openly and transparently sets out that 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.
While we would only consider using our nuclear weapons in the most extreme circumstances, we will remain deliberately ambiguous about precisely when, how and at what scale we would contemplate their use. As announced in the Integrated Review, we will also no longer give 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.
We will keep our nuclear posture, including our stockpile ceiling, under constant review, in light of the international security environment and the actions of potential adversaries. We can assure you the UK will keep working with international partners towards an environment in which further progress on nuclear disarmament is possible and remains committed to the long-term goal of a world without nuclear weapons. We firmly believe the best way to achieve this goal is through gradual multilateral disarmament negotiated using a step-by-step approach that takes account of the international security environment and is within the framework of the NPT. As we have explained previously (N10#2020/13304, dated 9 December 2020), the UK will not support, sign or ratify the Treaty on the Prohibition of Nuclear Weapons, as it fails to offer a realistic path to nuclear disarmament and risks undermining the effective non-proliferation and disarmament architecture we already have in place. Therefore, we will not be bound by its provisions.
The UK will continue to work for a successful NPT Review Conference that continues to lay the groundwork and helps build the trust and confidence necessary for multilateral disarmament, as well as strengthening the non-proliferation and peaceful uses pillars of the Treaty. We will continue to play a leading role in developing nuclear disarmament verification, on which our ability to achieve and maintain a world without nuclear weapons will depend. We will also continue to build trust and confidence amongst nuclear weapon states, and between nuclear weapon states and non-nuclear weapon states. As coordinator of the P5 Process (which brings together the five Nuclear Weapon States recognised under the NPT – China, France, Russia, UK and US – in a dedicated forum to discuss their responsibilities under the Treaty) in 2019 and 2020, we pushed forward work on transparency, leading the way with our consultation exercise on the UK’s national implementation report that has now been taken up by others, and securing agreement to a presentation by the nuclear weapon states of their national nuclear doctrines at the Review Conference. We look forward to continuing these discussions and picking up other important issues such as strategic risk reduction. As we approach the NPT Review Conference, we will continue to demonstrate our commitment to all pillars of the NPT, including disarmament.
Yours sincerely,
Defence Nuclear Organisation Secretariat
Trident Ploughshares is a campaign to disarm the UK Trident nuclear weapons system in a nonviolent, open, peaceful and fully accountable manner
