With threats to the British Isles and the Overseas Territories growing, should the UK focus on building a robust defensive shield to safeguard its territory and critical assets, or double down on expeditionary reach, deep-strike capabilities, and nuclear deterrence to keep threats far from its shores? This week’s Big Ask hinges on this strategic balance, as we asked six experts: Should Britain shift towards a more defensive military posture?
Honorary Fellow, Council on Geostrategy, Euro-Atlantic Security Specialist, and Former UK Defence Attaché to Moscow
Shield or sword: Does Britain need a more defensive military posture?
A heightened sense of the Russian threat to Britain has taken hold in the public consciousness. The Head of MI5 has warned that Russia is seeking to ‘unsettle’ Europe through ‘grey zone’ attacks short of launching a conventional conflict. Yet fear of the latter has been stirred by Russia’s war against Ukraine, concerns about the state of the British Armed Forces, and alarmist media reporting.
The UK must do more to defend itself. But there are significant dangers in overcorrecting toward a ‘Fortress Britain’. A defensive crouch would leave the country less secure, not more.
First, being overly defensive invites trouble. A posture built around, for example, hiding behind an ineffective ‘shield’ or ‘bastion’ surrenders the initiative to an adversary and would leave us open to coercion.
Second, the protection of Britain is more than the capacity to absorb punishment. Deterring Russia by threatening punishment is wiser and probably cheaper than relying on homeland defence if war breaks out. The challenge is achieving the right balance between offensive and defensive capabilities.
Third, the UK cannot insulate itself from attack. As during the Cold War, forward presence, intelligence sharing, allies, and the ability to strike targets at range can help prevent dangers from reaching home. Retreating from these commitments would weaken allied cohesion and give any adversary greater freedom of action.
Before the First World War, concern about the vulnerability of the homeland arguably clouded strategic judgement, distorted defence planning, and corroded those offensive capabilities that have repeatedly delivered advantage in the past. Britain shouldn’t make that mistake again. The choice is not between shield and sword. The UK needs both.
Research Fellow (National Security), Council on Geostrategy
Warfare in the missile age is a constant struggle of finding the right balance between offensive and defensive capabilities. The short answer is that though Britain does not need a more defensive posture overall, it does need to invest far more in its defensive capabilities. Air defences are one of the most significant capability gaps facing the UK today but erecting an impregnable umbrella is neither practical nor cost-effective.
The point of air defences should be to buy time for offensive capabilities to do their job in destroying an adversaries ability to continue launching strikes. But as the United States (US) and Israeli forces operating in Iran have shown, hunting the ‘archers’ is no easy feat even after air superiority has been achieved. As such, any investment in UK air defences should be focused on the most sensitive sites and the most likely threats. This means protecting sites such as Faslane, RAF Lossiemouth, and GCHQ from Russian ballistic missiles or cruise missiles which ‘leak’ through assets deployed further forward.
It is vital that this investment, however, does not become an opportunity cost for offensive capabilities. The ability to hunt Russian submarines and keep them bottled up beyond the Bear Gap (the stretch of water from Svalbard to Norway), to keep Russian aircraft at arms length, and to strike the enabling structure behind these platforms from missile factories to airbases and submarine pens also requires more investment. Without greater ability to hit back it would only be a matter of time before the umbrella cracks and lets the rain in.
Sir John Moore Adjunct Fellow in Military Affairs, Council on Geostrategy
As a general rule, the UK is best defended at reach through expeditionary forces, as these most ably support its NATO commitments. Russia is best deterred – and, if necessary, fought – closer to its own border, rather than on the British Isles, whether at land, sea, or in the air.
However, the call for improved homeland defences should not be dismissed. Britain has some serious vulnerabilities in terms of security, air defence, and civil protection. Key political, economic, and military sites are vulnerable to sabotage, interference and, in the worst case, missile strike. While the UK does not face the same threat as other frontline allies, all of its adversaries stock long-ranged cruise and ballistic missiles in their arsenal which can reach the British Isles. The UK currently has limited options that can reliably defeat this threat.
I have recently visited Kyiv, and experienced bombardment from Russian cruise and ballistic missiles firsthand. It is not a threat to be taken lightly. In case of a full-scale conflict, Russia could hit London, Faslane, Cheltenham, or Portsmouth using long-ranged ballistic missiles, disrupting key nodes in the British war effort.
As such, moderately increased investment in homeland air defence – especially against ballistic missiles – for key sites and creating a civil defence force would be sensible options to improve the security of the British Isles while the British Armed Forces take the fight to the enemy. The shield and sword are not mutually exclusive, but should instead complement each other for maximum effect.
Co-President (Research), Council on Geostrategy
The Kremlin would not fear a British anti-air missile shield. It knows it can fire hundreds if not thousands of missiles at British territories in Europe and that some will always get through. Even Israel’s expansive, integrated system – with close (Iron Dome), intermediate (David’s Sling), and long range (Arrow) defences – cannot intercept every missile or drone.
Insofar as Britain does need enhanced air defences, they should not be anchored to static silos on land. Rather, they should be delivered through a dispersed fleet of large autonomous anti-air vessels integrated into the New Hybrid Navy. Controlled from crewed warships or even the UK territories, these modular platforms would provide mobile air-defence pickets when required, while pivoting to offensive strike, sensing, and escort roles at other times. This prevents capital from being locked into single-use, purely defensive assets.
In any case, what Russia really fears is offensive firepower: the Royal Navy’s and Royal Air Force’s ability to launch devastating raids on Russian air stations, naval bases, radar facilities, and command and control systems, as well as energy and communications infrastructure. The Kremlin also respects escalation dominance: Russia’s doctrine exploits the rungs between conventional conflict and all-out strategic nuclear exchange – a flexible sub-strategic nuclear capability the British Armed Forces currently lack.
Britain should not attempt to turn itself into a solitary but tough little punch bag. Rather, it needs to think of itself as the pivot of a wider defensive formation. Frontline allies – Norway, Finland, Sweden, the Baltic states, Poland, Germany, Romania, and Turkey – are geographically positioned to provide NATO’s anti-access and area-denial (A2/AD) shield. The UK should champion their efforts while investing in long-range deep strike systems, agile naval mass, and a credible sub-strategic deterrent instead. That is what will deter Russia from miscalculation or outright attack.
François Crouzet Adjunct Fellow in Comparative Geopolitics, Council on Geostrategy
The issue is not so much about offence versus defence as it is about wars of choice versus wars of necessity.
The perennial problem of maintaining expensive armed forces in peacetime is that governments are tempted to use them as discretionary instruments of foreign policy, sometimes relying on rather convoluted arguments to establish a connection with national security. Arguably, the British public lost its appetite for such interventions some time between 2013 and 2018. One telling sign of this shift was the quiet disappearance of the word ‘expeditionary’ from the Franco-British Combined Joint Expeditionary Force in 2025. Conceived in 2010, the force belonged to the golden era of discretionary intervention, perhaps best epitomised by the 2011 Libya campaign.
Of course, the nuclear deterrent remains the bedrock of non-discretionary homeland defence. Much of the Royal Navy, alongside elements of the other services, contributes to its conventional underpinnings. There is substantial overlap between ‘making the deterrent safe’ and ‘making home waters safe’. Britain’s homeland is arguably less well protected against a conventional air threat than it was from the Second World War to the end of the Cold War, when a complex network of distributed radar stations and air stations protected its skies. However, it is difficult to imagine how a major conventional attack of that nature could remain separate from the risk of nuclear escalation.
Perhaps the most overlooked vulnerability, however, lies beneath the sea. Yes, Britain is an island nation. But no, it is not because 90% of its economy depends on goods arriving by sea. Tonnes are not pounds sterling, and imports are not Gross Domestic Product (GDP). Britain is overwhelmingly a services-based economy and, according to recent studies, an emerging AI powerhouse. It is therefore disproportionately dependent on the uninterrupted flow of international data, some 99% of which travels through submarine cables.
Perhaps it is time to reconsider the traditional assumption that protecting maritime trade – escorting container ships up and down the Red Sea, if need be – should remain the organising principle of a fleet built around ‘escorts’ and expeditionary operations, and the natural destination for the lion’s share of its budget. And perhaps it is those cables that are the new ‘Atlantic convoys’: the only thing that kept Sir Winston Churchill awake at night.
Junior Political Analyst, Serpens Centre for International Security
Britain should give greater priority to closing critical homeland defence gaps rather than expanding its ability to project power while its own territory and infrastructure remain vulnerable.
The Defence Committee has warned the UK has ‘next to nothing’ in integrated air and missile defence – even the Conservative Party’s proposed £10 billion may cover only a fraction of the investment required to build a comprehensive air-defence system. This suggests that continued investment in power projection without closing critical defensive gaps could leave Britain increasingly exposed and those gaps harder to address under attack.
Ukraine’s case suggests the competition is already skewed as strategically vital domains such as electronic warfare and anti-drone systems remain chronically underfunded while capital concentrates elsewhere. Considering Ukraine’s campaign is the most intensive real-world test of integrated air defence in modern warfare, data shows an attacker can generate more threats than a defender can afford to stop. To show the numbers: 281 interceptor drones costing roughly US$450,000 downed 258 Russian drones worth about US$25 million. The idea is not that cheap systems beat expensive ones, but that outcomes depend on allocating scarce assets across threat types by interception economics.
With contemporary threat landscape and warfare tactics, deterrence indeed remains necessary, but Ukraine’s experience shows that sustaining the fight requires reliable command and control, careful allocation of scarce interceptors, affordable interception and constant adaptation. The UK should prioritise closing defensive gaps while maintaining credible deterrence and expeditionary capabilities. Threats to overseas bases like Royal Air Force (RAF) Akrotiri show why the sword needs a shield.
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