UK national security: what have we learned from strategic defence reviews?

The history of British defence policy has been one of constant imbalance between resources, capability and commitments, interspersed with reviews that fail to solve the fundamental problems. These appraisals are typically done at times of economic crisis when public expenditure must be controlled.

The UK currently spends 2.3% of GDP on defence. This is above the European Union (EU) average but lower than the United States, where defence comprised 3.5% of GDP in 2023. But the new government has stated that it will set out the path to increasing spending to 2.5% of GDP (over an unknown time period).

Alongside this, the prime minister has commissioned a strategic defence review (SDR), due to report in the spring of 2025 (GOV.UK, 2024). The latest appraisal will ‘consider the threats Britain faces, the capabilities needed to meet them, the state of UK armed forces and the resources available’ (House of Commons Library, 2024).

The SDR is being conducted by Lord Robertson, former secretary of state for defence and former NATO secretary-general, together with General Sir Richard Barrons (former Commander Joint Forces Command) and Fiona Hill (previously a national security adviser to Donald Trump). They will have a team from the Ministry of Defence (MOD) and work closely with other government departments, notably HM Treasury.

It is important to note that the promised increase to 2.5% of GDP will be dealt with at a future fiscal event. As a result, choices made in the SDR – for example, about what to buy – must be made without knowing how much spending the Treasury will permit.

This is not new. The history of British defence policy has been one of constant imbalance between resources, capability and commitments, interspersed with defence reviews that do not solve the fundamental problems.

The Public Accounts Committee (PAC, 2021) reported: ‘The Permanent Secretary told us that in 2010 the defence budget had been made affordable, but at the expense of capability. Then in 2015, capability shortfalls were addressed but without sufficient funding. The budget was, therefore, constantly unbalanced in one way or another. He told us that he hoped now to develop a coherent and sensible package of capabilities which are backed up by resources, allowing the Department to plan properly in the longer-term’. His hopes were not realised, and the imbalances persisted.

Defence reviews have tended to be conducted at times of economic crisis when there is a need, as there is now, to control public expenditure. Consequently, they are often criticised as being budget-driven rather than threat-driven.

But in defence planning, these should be two sides of the same coin: the benefits from threat reduction should equal the opportunity cost of other potential uses of the budget. Currently, there are problems with both sides of the coin.

The MOD forecasts that during the ten years between 2032 and 2033, total planned defence spending will exceed the projected defence budget by £42.5 billion (National Audit Office, NAO, 2023).

Reviewing the lessons from the war in Ukraine, a House of Lords Committee found ‘that the UK’s Armed Forces lack the mass, resilience, and internal coherence necessary to maintain a deterrent effect and respond effectively to prolonged and high-intensity warfare’ (House of Lords, 2024).

What’s more, in announcing the SDR, the current defence secretary John Healey said that: ‘we need a new era for defence. Hollowed-out armed forces, procurement waste and neglected morale cannot continue’ (GOV.UK). Even the MOD recognises that the UK defence programme is currently both unaffordable and inadequate.

What broad questions should the latest strategic defence review address?

The SDR has to balance affordability (within a fragile fiscal position) against a general perception of increased threat, growing international insecurity and questions about military capability. The experiences of Houthi attacks on shipping in the Red Sea, Russia’s war in Ukraine and the poor performance of Israeli missile defences have together identified many vulnerabilities. These conflicts have highlighted the need for larger stockpiles of munitions and both more air-defence and anti-air-defence capabilities.

In principle, the defence planning process involves thinking forward to the security objective and then reasoning back through each of the stages that are needed to reach that objective. With this in mind, the questions that the SDR has to answer are:

What will be the UK’s role in the world and what are its associated vital interests?
What are the most likely threats to those interests?
How much can we rely on our allies, in particular Europe and the United States?
What are the capabilities (military or other) needed to meet the threats?
What are the forces needed to provide the required military capabilities?
What is the budget needed to provide those forces?
In a dynamic context, how can current readiness be balanced against investment in future capabilities?

The answer to most of those questions is ‘we have no idea’. Indeed, much of defence policy is reactive: responding to unpredicted threats from unexpected antagonists.

Previous defence reviews have charted a way forward that is rapidly reversed or outlined a future policy that is never implemented because the reviews are overtaken by real-world events (see House of Commons Library, 2024).

For example, the 1981 Nott review, which planned to reduce the size of the navy, was followed by the 1982 Falklands war, where the task force relied on vessels that were due to be scrapped. Similarly, the 1990 ‘options for change’ review, which planned cuts in conventional forces, was followed by their use in the 1991 Gulf war. And the 1998 SDR was followed by the interventions in Afghanistan and Iraq, while the 2021 ‘integrated review of security, defence, development and foreign policy’ was followed by Covid-19 and the Russian invasion of Ukraine, and had to be refreshed in 2023.

Chief of the General Staff, General Sir Patrick Sanders nicely captured the reactive nature of army objectives, stating: ‘I have served in, if you like, four Armies: one that was optimised for the cold war; one that was optimised for interventions, starting with humanitarian interventions in Sierra Leone and the Balkans, and then expanded into interventions in the Middle East; one that reset itself for counter-insurgency or stabilisation operations in Iraq and Afghanistan and, tactically, became extremely proficient and well prepared for it; and now an Army that is optimising for war and for warfighting’ (House of Commons Defence Committee, 2023). He did not mention the army in which he served during the Troubles in Northern Ireland.

How can decisions about defence policy be taken?

Given the unpredictability of threats and the impossibility of optimising against unknowns, a common analogy is to treat defence policy as an insurance policy. You do not know what may occur so you pay a premium, namely, a defence budget of some percentage of GDP, which is invested in such a way that it pays off.

This return could be reducing damage if an adverse event – such as a threat – materialises, or even deterring the threat. What the optimisation approach may regard as inefficient redundancy, is seen as useful through the insurance lens given the uncertainty: ‘just in case’ rather than ‘just in time’. But you cannot afford everything, so you have to choose.

One choice is between specialisation and diversification. Specialisation involves acquiring relatively few, expensive platforms – such as aircraft carriers – that are optimised for particular roles. These platforms have to be provided with arms, personnel, support, logistics and protection. But there is a danger that because there are so few of them, each platform is too valuable and too vulnerable to use.

Diversification, on the other hand, favours many ‘cheap and cheerful’ general-purpose systems that can be used for a variety of roles. The conflicts in which the UK has been involved over the past few decades – like the Falklands, the 1991 Gulf war, Iraq and Afghanistan – were largely ‘come-as-you-are-wars’ using whatever equipment was available at the time, not equipment optimised for a specific type of conflict.

If budget were not a concern, one might invest in both types of equipment. The United States, for example, was once able to develop both the cheap F16 fighter plane, which has been mass produced, as well as the expensive F15. But there is now rarely enough money to do both, even for the United States.

One can make a similar comparison between standard procurement processes and ‘urgent capability requirements’ (UCRs), which have different weightings of time, performance and cost from standard contracts. The procurement process for UCRs responds rapidly to unforeseen threats, to mission-critical operational risk or to essential safety requirements.

The urgency of these purchases prevents the normal acquisition process from being followed, and accepts that risk may be taken against performance, cost or coherence with wider defence equipment and activity programmes. When time is given priority, rapid procurement is possible.

What are the key choices that need to be made?

Within the general framework, the SDR needs to ask more specific questions, including:

Where should the UK commit its defence contribution, given that it can no longer afford to be a global player? Should it be continental Europe, the North Atlantic, the Middle East, the South China Sea or elsewhere in the world?
What are the likely forms of threats: conventional, nuclear or novel like cyber?
What are the capabilities needed to meet those threats: nuclear deterrent, ground forces, naval forces and/or air forces? And what enablers are needed to make the equipment effective? Within each of these broad classes, there are very concrete questions like should the aircraft and other platforms have people in them?

These are hard questions, which previous defence reviews have declined to answer. Rather, they have tried to maintain ‘balanced forces’ and a ‘global presence’.

Even when declaratory choices are made, they are not implemented. For example, many defence reviews since 1964 have announced the UK’s withdrawal from east of Suez. Yet after each withdrawal, commitments east of Suez creep back, and they are still there, as indicated in the constraints that the government has imposed on the 2024/25 SDR.

These constraints involve a total commitment to the nuclear deterrent; enhancing the UK’s contribution to NATO; reinforcing homeland security; supporting Ukraine; maintaining defence ties to the Indo-Pacific region, the Gulf and the Middle East; and delivering on the AUKUS partnership with Australia and the United States.

The government says: ‘Within these parameters, the Review will consider the need for prioritisation of objectives’. But if the parameters themselves are unaffordable and unachievable, trying to do all those things means not doing any of them effectively.

As a percentage of income, Britain has spent more on defence than comparable European countries, incurred too many commitments, bought weapons that are too expensive and failed to elaborate a security doctrine that can be sustained over the medium term. It seems unlikely that the new SDR will change any of that.