Select Committee on Defence Ninth Report


5  Nuclear deterrence in the 21st Century

Table 5: The UK still needs nuclear weapons to ensure its security: arguments for and against
For  Against 
The UK needs nuclear weapons as an insurance against an uncertain future. It is impossible to calculate what threats may emerge over the next 20 to 50 years, the lifetime of any successor to the UK's current Trident system.   
 Even the Government acknowledges there is no immediate nuclear threat in the post-Cold War world. The argument that a nuclear deterrent is required to defend against unknown future threats suggests that all states would be wise to possess nuclear weapons.  
It is possible that, over the next 20 to 50 years, a major nuclear threat to the UK might re-emerge. It is impossible to rule out a major shift in the international security situation in this timeframe which puts the UK under threat.   
 The threat analysis in the White Paper is weak. The threats analysed in the White Paper are not the most likely or dangerous threats the UK faces. For example, a nuclear deterrent cannot guard against the threat of climate change.  
It is possible that new nuclear states will emerge over the next 20 to 50 years which may pose a threat to the UK. The UK's nuclear deterrent provides an assurance that it cannot be subjected to future nuclear blackmail or a threat to UK security.   
 Yes, but there is no evidence that the UK will be a target of any state which might acquire nuclear weapons.  
There are limits to the extent to which intelligence can give prior warning of possible changes of intent by an existing or new nuclear weapon state. The lead-times and added cost of reconstituting any deterrent of the current capability may be greater than the speed of such a change.   
Nuclear weapons might have a deterrent effect against states sponsoring terrorism. The UK's nuclear deterrent may deter any state considering transferring nuclear weapons to terrorists.   
 It is implausible that terrorists, or even states supporting them, would be deterred by the remote threat of nuclear attack by the UK.  
The principles of nuclear deterrence hold good, despite the changes in the global environment. In terms of their destructive power, nuclear weapons pose a uniquely terrible threat and consequently have a capability to deter acts of aggression that is of a completely different scale from any other form of deterrence.  

 The nature of deterrence has changed fundamentally since the Cold War. The White Paper fails to give a convincing account of the role of deterrence in the current strategic context.  
Nuclear weapons have helped preserve peace and stability   
 There is no evidence that nuclear weapons have played a critical part in ensuring peace and stability.  
The UK needs to be vague about the circumstances in which it would use nuclear weapons, to keep our enemies guessing.   
 We need to know the broad kinds of circumstances in which the UK might use its nuclear weapons, if we are to judge if we should have them.  
The UK would only use its nuclear weapons in extreme circumstances, in self-defence, and in defence of its vital interests.   
 Terms such as extreme circumstances, self-interest and vital interests are meaningless without definition.  

The Government's approach to nuclear deterrence

65. The White Paper states that "the fundamental principles relevant to nuclear deterrence have not changed since the end of the Cold War, and are unlikely to change in future".[83] It maintains that because nuclear weapons "pose a uniquely terrible threat," they "have a capability to deter acts of aggression that is of a completely different scale to any other form of deterrence". On that basis, it concludes that "nuclear weapons remain a necessary element of the capability we need to deter threats from others possessing nuclear weapons".[84]

66. The White Paper goes on to describe "five enduring principles" which, it says, "underpin the UK's approach to nuclear deterrence." These include:

  • a focus on "preventing nuclear attack";
  • a commitment to a "minimum" deterrent;
  • the maintenance of deliberate ambiguity about the use of nuclear weapons;
  • a commitment to the nuclear defence of the UK's NATO allies; and,
  • the maintenance of the UK as "an independent centre of decision-making" which "enhances the overall deterrent effect of allied nuclear forces".[85]


67. Some witnesses to our inquiry have questioned the Government's understanding of nuclear deterrence. Nick Ritchie, of the University of Bradford, argues that the Government's contention that the fundamental principles of nuclear deterrence have not changed since the end of the Cold War is "an assertion, a point of view". He maintains that nuclear deterrence is a "contested concept" and that "the "principles" of nuclear deterrence are not objective truths" but rather "theoretical concepts"." He says that "the Government's assertion is not necessarily wrong, but it does not provide any evidence for its case".[86]

68. Dr Stephen Pullinger, of the International Security Information Service, for example, challenges the White Paper's statement that the fundamental principles of nuclear deterrence have not changed since the end of the Cold War. He argues that although "the fundamental principles may not have changed…this should not be interpreted to mean that the Cold War deterrence model can be transposed to each and every other future scenario in which nuclear weapons are a factor".[87] Dr Pullinger argues that the context within which nuclear deterrence now operates is very different from that of the Cold War. On that basis, he questions whether the UK's nuclear weapons can any longer play a useful and credible role.

69. Dr Jeremy Stocker, of the IISS, agrees and states that "absent an overwhelming threat such as the Soviet Union, the credibility of a nuclear response to limited aggression must be in doubt".[88] In evidence to us, Dr Stocker maintained that, ultimately, "deterrence and particularly its nuclear dimension is as relevant as it was in the Cold War". But he argued that "the nature of that deterrence has changed fundamentally…for the UK probably more than anybody else, with the possible exception of France". He suggested

The context within which we might have to conduct deterrence in the future, other than in the scenario of a resurgence of a hostile Russia, has changed completely and all of the kind of assumptions and policies that we worked out during the Cold War and learned quite painfully and over a protracted period of time, most of those assumptions no longer apply.

Dr Stocker concluded that "deterrence is as salient as it ever was, but it is a very, very different kind of deterrence.[89] The White Paper, he suggested, "does not deal with some fundamental challenges to deterrence in the "second nuclear age"—the post-Cold War age in which nuclear proliferation has taken hold. In evidence to us, Dr Stocker argued that "the White Paper really says very little about deterrence". He suggests that "in order to argue the Government's case…the Government probably does have to do considerably more in spelling out a deterrence policy as well as a policy for the deterrent, which is actually what the White Paper is all about".[90] In his written memorandum, he notes that "no comprehensive review of post-Cold War deterrence needs has been conducted, certainly not in public" and he suggests that "now may be as good a time as any" for that review.[91]

70. Sian Jones, of the Aldermaston Womens' Peace Campaign, argued that the "security agenda has changed" since the end of the Cold War and that nuclear deterrence was an "outmoded concept".[92] Dr Rebecca Johnson also calls for a review of nuclear deterrence and argues that the White Paper "fail[s] to justify its premise that our nuclear weapons aided peace and international security and deterred acts of aggression against the UK". She maintains that "too much of our future security is at stake to rely on cold war myths and voodoo mantras about deterrence". And she suggests that "the Government needs to provide and examine evidence from the real world" to support its contention that nuclear weapons are effective in deterring aggression. Dr Johnson concludes that "even if nuclear weapons did play a role in deterring war among the major powers, relying on them in the manifestly different conditions the UK now faces reveals a naïve and complacent stretch of faith". She, therefore, calls upon Parliament to "insist on seeing a deeper analysis of nuclear and non-nuclear deterrence".[93]

71. RUSI witnesses too see a need for a more comprehensive analysis of the meaning and role of nuclear deterrence. In evidence to us, they state that

the debates around the White Paper would benefit from an assessment of what deterrence is, how it is achieved, what are the implications of deterrence theory and practice of the changed strategic environment, and what are the circumstances in which nuclear deterrence might be relevant.[94]

72. In a similar vein, the Church of England questions "whether post-Cold War, deterrence will work". And it asks "can those states and non-state actors that threaten UK security actually be deterred from undertaking acts of aggression by either new or existing approaches to nuclear deterrence". According to the Church of England, "this needs to be much more fully argued than in the current White Paper".[95]

73. We asked the Secretary of State for Defence whether there was a case for reassessing the role of nuclear deterrence in light of the changed international circumstances of the post-Cold War world. Mr Browne told us that the relevance of nuclear deterrence did not end with the passing of the Cold War. The nuclear weapons, he argued, remained relevant and stated that "I fundamentally do not believe that deterrence is an outmoded concept," despite the changes which had occurred in the international system since the Cold War. In fact, he maintained that it was the continually changing nature of the threat that warranted the UK's continued possession of nuclear weapons, as "history tells us that countries' intentions…can change very, very quickly".[96] He argued that "deterrence is not that sophisticated a concept" and suggested that the problem was that "we have over sophisticated it because it has always been associated with nuclear weapons".[97]

74. The White Paper states that the concept of deterrence has not changed since the end of the Cold War and it outlines the underlying principles which shape the UK's current approach to nuclear deterrence. Some witnesses to our inquiry questioned the continuing relevance of nuclear deterrence while others argued that it remained as relevant as it ever was during the Cold War. The Government should do more to explain what the concept of deterrence means in today's strategic environment.


75. The White Paper states that "we deliberately maintain ambiguity about precisely when, how and at what scale we would contemplate use of our nuclear deterrent". It maintains that the Government "will not simplify the calculations of a potential aggressor by defining more precisely the circumstances in which we might consider the use of our nuclear capabilities". On that basis, it states that "we will not rule in or out the first use of our nuclear weapons".[98] The White Paper states that the UK would use nuclear weapons in response to threats to its "vital interests" and in defence of its NATO allies.[99]

76. Witnesses from RUSI argue that maintaining ambiguity about the circumstances in which the UK might use nuclear weapons is understandable and enhances the deterrent effect. In their memorandum to us, the RUSI witnesses maintained that

In the Cold War, British deterrence policy was based on the certainty of response…Today, with more numerous and more diverse potential threats, this uncertainty in threat is offset by strategic ambiguity and uncertainty in Britain's response: no potential adversary could be absolutely certain that Britain would not respond, an uncertainty which increases significantly the complexity of an adversary's decision-making.[100]

77. Some witnesses to our inquiry, however, challenged the Government's deliberate ambiguity. Professor William Walker, of the University of St Andrew's, argues that although it is understandable why the Government avoided naming specific states as future threats, the White Paper "should nevertheless have provided clearer indication of the kinds of future circumstances that would compel the UK to threaten nuclear attack in its own defence".[101] Similarly, in evidence to us, Dr Stephen Pullinger argued that "there has been too much ambiguity about the circumstances" of use of nuclear weapons. He maintains that "the language we are using…is giving an awful lot of leeway to the circumstances in which we would use nuclear weapons".[102]

78. The Church of England states in its memorandum to us that "given the grave ethical issues involved with any use or threat of use of nuclear weapons, it is legitimate to ask in a democracy…in what sorts of circumstances their use might be justified and proportionate". It maintains that "to assess the validity of the deterrence argument…there must be some indication of the circumstances in which the weapons might be used". According to the Church of England, this would not require the Government to disclose secret targeting information or precise circumstances of use. Instead, it states that "all it would require is for the Government to indicate what is its overall strategy, including the parameters for the weapons' use and any limits within which any targeting would be set".[103] It states that the French, for example, outline their strategy for targeting an aggressor's political, economic and military power centres, and not its civilian centres. It concludes that "it is disappointing that a similar shift in strategy and a move towards greater public transparency is not reflected in the White Paper".[104]

79. When discussing the legality of threats to use nuclear weapons, Professor Haines told us that one of the problems is

you can talk about as many hypothetical situations as you like; what we will eventually be faced with will be something quite different, and if you base everything on your range of hypothetical situations that you are teasing out you will probably get it wrong.[105]

80. We asked the Secretary of State for Defence whether he could clarify the circumstances in which the UK would consider using its nuclear deterrent. He stated that the UK "would only consider using nuclear weapons in self defence" and "only…in extreme circumstances". He insisted that "it is, and always has been, part of our deterrence posture that we retain an ambiguity about precisely when, how and at scale we would contemplate using our nuclear weapons". "Keeping the enemy guessing," he insisted, was "all part of deterrence".[106] For the same reason, Mr Browne declined to define what the White Paper meant by the UK's "vital interests," saying that "if we had wanted to put [a definition] into the public domain, we would have put one in…the White Paper".[107]

81. The Government has stated that the UK will use its nuclear weapons only in "self-defence", in "extreme circumstances", and in defence of the UK's "vital interests", but has not defined these terms. It argues that it is important to maintain ambiguity about the exact circumstances in which the UK might use its nuclear weapons. Although we understand the need for ambiguity, the Government should be clearer that this ambiguity does not lead to a lowering of the nuclear threshold.


82. The 1998 Strategic Defence Review stated that in order to be a credible deterrent, "Trident must…be capable of fulfilling [a] "sub-strategic" role". In our first report on the future of the UK's strategic nuclear deterrent, we characterised a sub-strategic strike as one which would involve the launch of one or a limited number of missiles against an adversary as a means of conveying a political message, warning or demonstration of resolve. But we noted that a sub-strategic role should not be confused with a tactical role and that Trident was not designed or intended to fulfil a tactical role on the battlefield.[108]

83. The White Paper makes no reference to sub-strategic deterrence. This omission is noted in several submissions to our inquiry. Professor Paul Rogers, of the University of Bradford, for example, argues that "given that the Government seeks a public discussion on the replacement of Trident prior to the vote in Parliament, it is perhaps unfortunate that this core aspect of the UK nuclear posture gets so little attention".[109]

84. The White Paper does emphasise the importance of lower yield nuclear warheads in making deterrence against smaller nuclear threats more credible. It states that "the ability to vary the numbers of missiles and warheads which might be employed, coupled with continued availability of a lower yield from our warhead, can make our nuclear forces a more credible deterrent".[110]

85. In evidence to us, Dr Pullinger argues that "there is a danger…that the deployment of lower yield warheads…will lower the nuclear threshold and increase the likelihood of nuclear use to achieve more limited, war-fighting objectives". In this sense, he notes, "the sub-strategic function becomes a tactical one".[111]

86. We asked the Secretary of State whether the Government was still committed to a sub-strategic role for Trident. He told us that the UK's nuclear weapons "are not intended, nor are they designed, for military use during conflict". He stated that "we have deliberately chosen to stop using the term "sub-strategic Trident". In the past, "it was applied to a limited use of our weapons".[112]

87. The Government says it no longer uses the term "sub-strategic" in discussing the UK's nuclear weapons. However, the White Paper refers to varying the yield of the UK's nuclear warheads. We call upon the Government to clarify how a reduced yield differs from a sub-strategic role. The Government should also state why a sub-strategic role was thought necessary in 1998 but is no longer necessary now.


88. The White Paper states that "the UK's nuclear deterrent supports collective security through NATO for the Euro-Atlantic area". And it maintains that "nuclear deterrence plays an important part in NATO's overall defensive strategy" and that "the UK's nuclear forces make a substantial contribution" to that strategy.[113] In exchange of letters between the UK and the United States, on 7 December 2006, the Prime Minister states that

as has been the case in the past with the Polaris force, and is currently the case with out Trident force, we intend that a future UK deterrent submarine force equipped with Trident, and any successor to Trident, will be assigned to the North Atlantic Treaty Organisation: and expect where the United Kingdom Government may decide that supreme national interests are at stake, this successor force will be used for the purposes of international defence of the Atlantic Alliance in all circumstances.[114]

89. In evidence to our inquiry, Professor Rogers states that despite the end of the Cold War, the UK's nuclear weapons "remain committed to NATO" and notes that "NATO nuclear planning still involves a policy of first use" of nuclear weapons.[115] RUSI told us that "Britain's nuclear deterrent remains an important element of the European contribution to NATO, with its sub-strategic policy a central element of NATO's deterrent strategy". But it states that "NATO's doctrine of sub-strategic deterrence remains largely under-developed since the end of the Cold War". It argues that "the Government will need to clarify the precise role of sub-strategic Trident in the NATO context".[116] The need for further clarity about the role of UK nuclear weapons in a NATO context is also raised by Abolition 2000, which asks "whether the declared NATO policy of potential first use…is consistent with UK policy and UK responsibilities in international law".[117] Similarly, Scottish CND suggests that "the role of nuclear forces in NATO today is by no means clear".[118]

90. The Government states that the UK's nuclear deterrent will continue to be assigned to NATO. NATO nuclear doctrine, however, explicitly involves a policy of not ruling out first use of nuclear weapons and a policy of sub-strategic deterrence. We call upon the Government to clarify, in time for the debate and vote in the House of Commons, how the UK's nuclear forces are integrated into the nuclear defence of NATO and what the implications of the Alliance's first use and sub-strategic policies are for the UK's nuclear deterrent.

The Government's rationale for retaining a nuclear deterrent

An insurance against an uncertain future

91. The White Paper states that the central argument for retaining the deterrent is an insurance "against an uncertain future". The White Paper states that "there are limits to the extent to which intelligence can inform us about medium to long-term changes in the nuclear capabilities of others, or give prior warning of a possible change in intent by an existing nuclear weapon State". It maintains that "we must…be realistic about our ability precisely to predict the nature of any future threats to our vital interests over the extended timescales associated with decisions about the renewal of our nuclear deterrent".[119] Looking ahead to the period 2020 to 2050, the time in which any future deterrent system would operate, the White Paper highlights "some trends that give rise to significant causes for concern". It identifies nuclear proliferation as a particular concern which, it says, "potentially could lead to increasing levels of international instability and risk of interstate conflict". Although the White Paper acknowledges that the UK does not face a current nuclear threat, it argues that there is "the possibility that, at some stage in the future, nuclear capabilities and hostile intent will become dangerously aligned".[120] The Government foresees three specific possibilities: the re-emergence of a major nuclear threat; the emergence of new nuclear weapon states; and the possibility of state-sponsored terrorism.[121]

92. Witnesses to our inquiry offered widely differing views on the rationale offered by the Government for retaining a nuclear deterrent. RUSI, for example, agrees with the Government that "the future strategic environment remains unknown and unknowable". It argues that

The rationale for maintaining the nuclear deterrent is based on the existence of nuclear arsenals in at least eight other states, the fact that nuclear technologies, know-how and desires are proliferating, the implicit assumption that more states are likely to acquire nuclear weapons in the future, the risks of rogue states and terrorist organizations acquiring nuclear and other weapon of mass destruction capabilities, and the calculation that nuclear aggression realistically can only be deterred by the possibility of nuclear retaliation.[122]

93. Professor William Walker, of St Andrew's University states that the White Paper contains "general descriptions of possible developments in the international arena which cannot be discounted". However, he argues that the document is "extremely vague" and that "little effort is made to explain how and why they pose particular threats to the UK, and why—if the threats do exist today—they are sufficiently tangible and probable to merit paying such a heavy insurance premium".[123]

94. The Nuclear Information Service argued that "to equate Trident with an insurance policy is a simile that falls at the slightest examination". It argues that "insurance is recommended for everybody, not just the few" and that "to pursue the insurance analogy would be to accept that every country was entitled to it".[124] Similarly, CND suggest that "the White Paper outlines an appalling string of possibilities" and argues that the logic of its insurance argument risks "reinforcing the notion that building more weapons of mass destruction provides security." It concludes that "through its short-sighted actions, the Government is contributing to nuclear escalation and eventual nuclear war".[125]"

95. Greenpeace argues that the Government's assessment of future threats is flawed. It argues that "needed now are not new rationales for possessing nuclear weapons but increased diplomatic effort and initiatives to rid the world of nuclear weapons". According to Greenpeace, the Government focuses on the wrong threats. It states that "we fail to see how nuclear weapons will halt the impact of climate change, ensure adequate birth control for the world's poor or make any nation economically richer and not poorer". And it argues that the UK's continued possession of nuclear weapons risks perpetuating and heightening the threat of nuclear proliferation for "as long as there are nuclear materials and technology available and…nuclear weapons are regarded as being essential to the security of a few nations, there will remain a risk of further proliferation of nuclear weapons".[126]

96. Dr Andrew Dorman, of King's College London, maintains that "the Government's case although repackaged remains the same as that confronting the Attlee Government in 1946," that "in an uncertain world, the United Kingdom needs to have the ultimate insurance policy that a nuclear deterrent is seen to bring".[127] He suggests that "the deterrence argument was easier to make when there was an obvious potential foe in the form of the Soviet Union". He argues that "when, as the White Paper suggests, it involves non-state actors, such as al-Qaeda, it is far harder to justify".[128]


97. The White Paper envisages a role for the UK's nuclear deterrent in deterring state-sponsored terrorism. It states that "while our nuclear deterrent is not designed to deter non-state actors, it should influence the decision-making of any state that might consider transferring nuclear weapons or nuclear technology to terrorists".[129] It also states that

we make no distinction between the means by which a state might choose to deliver a nuclear warhead, whether, for example, by missile or sponsored terrorists. Any state that we can hold responsible for assisting a nuclear attack on our vital interests can expect that this would lead to a proportionate response.[130]

The White Paper also says that

A key element of our ability to exercise effective deterrence in such circumstances is our capability precisely to determine the source of material employed in any nuclear device. We will retain and strengthen the world leading forensic capability at the Atomic Weapons Establishment, Aldermaston in this area.[131]

98. Some witnesses to our inquiry expressed scepticism about the relevance of the UK's nuclear deterrent in deterring state-sponsored terrorism. Dr Rebecca Johnson argues that "the nuclear threat in these cases would be far less likely to deter than existing collective political, diplomatic and economic tools, and any nuclear use could profoundly compromise Britain's security and international standing in the longer-term". She suggests that extremist groups would not be deterred by nuclear weapons and that, in fact, "their game plan could include provoking a nuclear or similarly disproportionate retaliation in order to turn moral outrage against the retaliator and recruit more people to their causes".[132] Professor John Baylis argues that nuclear deterrence is "not likely…[to] work against non-state terrorist groups". However, he suggests that "in circumstances where it is clear that the terrorists are operating from a particular territory, then deterrence aimed at the government of that state might work but this invariably will not be the case".[133]

99. We asked the Secretary of State how the UK's nuclear deterrent would be relevant in deterring state-sponsored terrorism. Mr Browne told us that "we might face at some time in the future a rogue state which has [a nuclear] capability and may want to use terrorists as proxies as a way of launching weapons against us". This, he maintains, is what the White Paper seeks to convey. He stated that "we are not saying that we would deploy this as a deterrent or as an answer to what people would generally consider to be the terrorist threat". The White Paper, Mr Browne insisted, defined a specific type of terrorist threat and asserted its relevance in that context. The Government, he said, did not regard the nuclear deterrent as an effective deterrent against terrorists themselves, but rather against states sponsoring terrorism.[134]

100. The Government acknowledges that there is no current nuclear threat to the UK but argues that nuclear weapons are needed as an insurance policy against an uncertain future. Some of our witnesses pointed to nuclear proliferation and noted that nuclear aggression could only be deterred by the possibility of nuclear retaliation. Others—including some who accepted the need for the deterrent—felt that the Government's analysis of the threat was vague, flawed and otherwise lacked logic, and many particularly expressed scepticism about the efficacy of the deterrent in countering state-sponsored terrorism.

83   Cm 6994, para. 3.3, p 17 Back

84   Ibid. Back

85   Cm 6994, para. 3.4, pp 17-18 Back

86   Ev 141 Back

87   Ev 101 Back

88   Ev 109 Back

89   Q 172 Back

90   Q 173 Back

91   Ev 109 Back

92   Q 17 Back

93   Ev 192 Back

94   Ev 114 Back

95   Ev 176 Back

96   Q 353 Back

97   Ibid. Back

98   Cm 6994, para 3.4, p 18 Back

99   Ibid. Back

100   Ev 114 Back

101   Ev 165 Back

102   Q 182 Back

103   Ev 177 Back

104   Ibid. Back

105   Q 287 Back

106   Q 355 Back

107   Ibid. Back

108   HC (2005-06) 986, para 41, pp 12-13 Back

109   Ev 113 Back

110   Cm 6994, para. 4.9, p 23 Back

111   Ev 105 Back

112   Q 358 Back

113   Cm 6994, para 3.4, p 18 Back

114   Exchange of letters between the Prime Minister and the US President, 7 December 2006 Back

115   Ev 130 Back

116   Ev 117 Back

117   Ev 132 Back

118   Ev 87 Back

119   Cm 6994, para 3.5, p 18 Back

120   Cm 6994, para 3.8, p 19 Back

121   Cm 6994, paras 3.5-3.12, pp 18-19 Back

122   Ev 114 Back

123   Ev 165 Back

124   Q 123 Back

125   Ev 80 Back

126   Ev 186 Back

127   Ev 182 Back

128   Ibid. Back

129   Cm 6994, para 3.11, p 19 Back

130   Ibid. Back

131   Cm 6994, para 3.12, p 19 Back

132   Ev 192 Back

133   Ev 125 Back

134   Q 362 Back


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