Deterrence as part of the UK’s defence policy

Approximate read time: 10 minutes

On 31 October 2024 the House of Lords will consider the following question for short debate:

Lord Trefgarne (Conservative) to ask His Majesty’s Government whether deterrence remains a core element of the United Kingdom’s defence policy.

1. What is meant by deterrence in a defence context?

In simple terms, the term deterrence can be defined as the practice of discouraging or restraining someone—in a defence context, usually a nation-state—from taking unwanted actions, such as an armed attack.^[1] It involves an effort to stop or prevent an action from occurring (such as deterring an army from crossing an international border). As opposed to what is sometimes called ‘compellence’, or the attempt to force a given actor to do something (perhaps forcing that same army to retreat from the border region through the use of force or threats).

The concept of deterrence can also arguably be applied to two sets of circumstances.^[2] The first is direct deterrence, which consists of efforts by a state to prevent attacks on its own territory. The second is extended deterrence, which involves discouraging attacks on third parties, such as allies or partners. US defence analyst Michael J Mazaar notes that extended deterrence is often the more difficult to achieve:

[E]xtended deterrence is more challenging than direct deterrence. This is partly true for military operational reasons: It is more difficult to deny an attack far from home, a mission that demands the projection of military force sometimes thousands of miles away and often much closer to the territory of the aggressor state. However, it is also true for reasons of credibility. An aggressor can almost always be certain a state will fight to defend itself, but it may doubt that a defender will fulfil a pledge to defend a third party. During the cold war, for example, there were constant debates about the credibility of the US promise to “sacrifice New York for Paris”.^[3]

Some analysts also distinguish between the concepts of ‘general’ deterrence, which is the ongoing and involves persistent effort to prevent unwanted actions over the long term and in noncrisis situations, and ‘immediate’ deterrence, which represents more short-term urgent attempts to prevent a specific, imminent attack, most typically during a crisis.^[4]

In its 2019 note on the doctrine of deterrence, the Ministry of Defence uses the following definition, which also takes into account the “political will” to act:

[Deterrence is] [t]he convincing of a potential aggressor that the consequences of coercion or armed conflict would outweigh the potential gains. This requires the maintenance of a credible military capability and strategy with the clear political will to act.^[5]

2. How has the UK’s defence policy historically exemplified the concept of deterrence?

The concept of deterrence has arguably permeated through several aspects of the UK’s defence policy since the second world war. It is evident in the UK’s approach to nuclear weapons capabilities and its membership of multilateral alliances such as the NATO.

2.1 UK’s nuclear deterrent

Guidance published by the Ministry of Defence (MOD) in May 2024 (under the previous government) notes that the view of successive UK governments is that “a minimum, credible, independent nuclear deterrent, declared to the defence of NATO, is essential to our security and that of our NATO allies”.^[6]

Since April 1969, the Royal Navy has maintained continuous at sea deterrence, with at least one nuclear-armed ballistic missile submarine patrolling the seas undetected at all times.^[7] Known as the continuous at sea deterrent (CASD), the MOD states that its “fundamental purpose is to preserve peace, prevent coercion, and deter aggression”. They add that the UK maintains only the minimum amount of destructive power needed to guarantee our deterrent remains credible and effective against the full range of state nuclear threats.

The UK’s nuclear deterrent is operationally independent. Only the prime minister can authorise the use of the UK’s nuclear weapons even if deployed as part of a NATO response. The MOD suggests that the UK would consider using nuclear weapons “only in extreme circumstances of self-defence, including the defence of our NATO allies”.

2.2 International alliances and membership of NATO

The UK has close bilateral relationships with several nations on defence matters, including the United States, for example, as well as European partners such as France. These relationships are often expressed in terms of working together to combat and provide a deterrent towards perceived external threats, including the influence of hostile states.^[8]

The UK is also a member of international alliances that promote deterrence as part of their core doctrine, the foremost of which is NATO. NATO itself defines key elements of its role as “preventing conflict and war, protecting allies, maintaining freedom of decision and action, and upholding the principles and values it stands for”, which include individual liberty, democracy, human rights and the rule of law.^[9] NATO officials contend that free societies and the rules-based international order “need to be backed by credible transatlantic defence”.

NATO’s deterrence and defence posture is based on an “appropriate mix” of nuclear, conventional and missile defence capabilities, complemented by space and cyber capabilities.^[10] At the 2022 Madrid summit, NATO set a new baseline for its deterrence and defence posture in line with its “360-degree approach, across the land, air, maritime, cyber and space domains, and against all threats and challenges”.^[11] This was followed at the 2023 Vilnius summit with the agreement of new measures to “enhance NATO’s deterrence and defence in all domains”, including a new generation of regional defence plans to strengthen forward defences and “increase the alliance’s ability to rapidly reinforce any ally that may come under threat”.

The concept of deterrence is also present in the UK’s AUKUS partnership with the United States and Australia. Agreed in 2021, AUKUS is a trilateral security partnership focused on supporting Australia in acquiring its first conventionally armed, nuclear-powered submarine fleet, and to enable close cooperation on key defence technologies, including cutting-edge advanced capabilities such as artificial intelligence.^[12] Seen particularly as a response to the rising influence of China, a 2023 joint statement by the three partner nations stated that a key purpose of AUKUS will be to contribute to “integrated deterrence” by pursuing layered and asymmetric capabilities that promote increased security and stability.^[13]

3. What was the previous government’s approach to deterrence?

In March 2023, the Conservative government published an update to its earlier 2021 integrated review (IR) of defence and foreign policy.^[14] The concept of deterrence was contained within both IR2021 and IR2023 documents and in the 2023 integrated review strategic framework published alongside the 2023 integrated review refresh. Indeed, it formed a key element of one of the four pillars that the framework stated were at the core of the government’s approach:

Deter, defend and compete across all domains. This pillar reinforces the ongoing shift to an integrated approach to deterrence and defence, to counter both state threats and transnational security challenges. It reaffirms that NATO is at the core of this effort, but is clear that—given the changing threat picture—effective deterrence will mean working through other groupings and beyond the Euro-Atlantic theatre. It also introduces a renewed emphasis on the concept of strategic stability—establishing new frameworks and building a new international security architecture to manage systemic competition and escalation in a multipolar environment.^[15]

IR2023 said that the UK would take an integrated approach to deterrence and defence, including its nuclear weapons:

The foundational component of an integrated approach to deterrence and defence remains a minimum credible, independent UK nuclear deterrent, assigned to the defence of NATO. It ensures that potential adversaries can never use their capabilities to threaten the UK or our NATO allies or to deter us from taking the action required to maintain regional and global security and stability. We would consider using our nuclear weapons only in extreme circumstances of self-defence, including the defence of our NATO allies.^[16]

Deterrence was also a thread that ran through many further areas of the review including the UK’s conventional, cyber and space forces. IR2023 stated these elements of the UK’s defence capabilities must be “sufficiently capable, resilient, deployable and adaptive to deter potential adversaries from engaging in conflict, and to win a conflict if deterrence fails”.^[17] IR2023 also noted the importance of bilateral and multilateral alliances in its approach, stating that “across the full range of state and non-state threats, burden-sharing with our allies and partners is a vital element of an integrated approach to deterrence and defence”. The review singled out the UK’s relationships with the US and France in particular, as well as the UK’s contribution towards and membership of NATO.

4. What has the current government said about deterrence in UK defence policy?

In both the period before and since this year’s general election, Labour figures have committed to various aspects of the UK’s deterrence approach. This includes the UK’s membership of NATO and the UK’s nuclear deterrent.

Labour’s general election manifesto cited the importance of the UK’s role in NATO, arguing that Labour’s commitment to NATO as the cornerstone of European and global security was “unshakeable”.^[18] The manifesto also pledged to seek an “ambitious” new UK-EU security pact to strengthen cooperation against common threats. The manifesto added that a Labour government would “rebuild relationships with key European allies, including France and Germany, through increased defence and security cooperation”. Further, it stated that the UK will seek new bilateral agreements and closer working with Joint Expeditionary Force partners. The manifesto also stated that a Labour government would remain committed to the AUKUS security partnership.

In addition, Labour’s election manifesto stated that a Labour government’s commitment to the UK’s nuclear deterrent was “absolute”.^[19] Labour has also committed to what it calls a ‘triple-lock’ commitment to the UK nuclear submarine programme, which includes the following pledges:

• building four new nuclear submarines in Barrow-in-Furness, supporting high-quality, high-status apprenticeships and jobs, with the supply chain benefits being felt right across the country
• Britain maintaining its continuous at-sea deterrent, 24 hours a day, 365 days a year—securing protection for both the UK and NATO allies
• the delivery of all future upgrades needed for those submarines to patrol the waters and keep our country safe^[20]

Labour ministers have reiterated such commitments since taking office. For example, Foreign Secretary David Lammy and Defence Secretary John Healey published a joint article in July 2024 where they spoke of the importance of NATO in deterring Russian aggression in particular and of the importance of maintaining the UK’s nuclear defence capabilities.^[21] The government has committed to a ‘NATO-first’ defence policy, including defence procurement.^[22]

Labour has also launched a new strategic defence review (SDR). The terms of reference for that review, published 17 July 2024, said that the SDR “will determine the roles, capabilities and reforms required by UK defence to meet the challenges, threats and opportunities of the twenty-first century”.^[23] It stated that one of the themes the SDR will examine is the “UK’s international partnerships and alliances, and how these can be strengthened in the cause of collective security and deterrence”.

5. Read more

• Ministry of Defence, ‘Deterrence: The defence contribution’, 2019
• Defence Science and Technology Laboratory, ‘UK Deterrence and Assurance Academic Alliance (DAAA)’, updated September 2024
• Foreign, Commonwealth and Development Office and Ministry of Defence, ‘This government will have a ‘NATO first’ defence strategy: Article by the foreign secretary and defence secretary’, 9 July 2024
• NATO, ‘Deterrence and defence’, 1 July 2024

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Cover image by DON JACKSON-WYATT on Unsplash