The question facing ministers is not simply how much Britain spends on defence, but how effectively that money is spent. In an increasingly dangerous world, closer UK–European defence cooperation must be central to the answer. 

By Sir Nick Harvey, CEO, European Movement UK 

The resignation of John Healey as Defence Secretary should send shockwaves through Westminster. 

Defence Secretaries do not resign lightly, particularly at a time of war in Europe, growing instability in the Middle East and mounting pressure on Britain's armed forces. Yet Healey concluded that he could no longer support the government's delayed Defence Investment Plan, reportedly warning that the funding settlement being offered was inadequate for the scale of the threats Britain faces. 

His departure follows reports that the Chief of the Defence Staff, Air Chief Marshal Sir Rich Knighton, also felt compelled to write directly to the Prime Minister amid concerns that the resources under discussion would fall short of Britain's defence requirements. 

Taken together, these developments reveal more than a disagreement over budgets. They expose a deeper challenge facing Britain as it seeks to define its place in an increasingly dangerous world. 

There is no doubt that Britain needs to invest more in defence. Russia's invasion of Ukraine continues to threaten European security. Cyber attacks, economic coercion and hybrid threats are becoming ever more commonplace. The strategic assumptions that shaped the post-Cold War era are rapidly disappearing. 

But there is another reality that policymakers must confront honestly. 

For more than seventy years, European security rested upon a simple assumption: that the United States would ultimately underwrite the defence of the continent. That assumption can no longer be taken for granted. 

This is not a criticism of our American allies, whose contribution to European security has been immense. But the geopolitical realities of the twenty-first century are changing. Washington's strategic focus is increasingly directed towards the Indo-Pacific and the challenge posed by China. Successive American administrations have urged European nations to take greater responsibility for their own defence and security. 

NATO remains the cornerstone of our collective defence and will continue to do so. Yet the era of a Pax Americana, in which Europe could assume that the United States would always provide the decisive military backstop, is coming to an end. The guarantee remains, but the certainty that once surrounded it has weakened. 

That reality should shape every aspect of Britain's Defence Investment Plan. 

If Europe is expected to shoulder a greater share of responsibility for its own security, then it follows that Britain cannot think about defence purely through a national lens. We must begin with a recognition that our security is inseparable from that of our European neighbours. 

In the harsh realities of today's world, Europe is not simply one option among many. It is the arena in which Britain's security will be won or lost. When it comes to defence planning for the decades ahead, Europe is the only game in town. 

This is where the debate raised by Healey's resignation becomes especially important. 

If resources are constrained, as both Healey and Sir Rich Knighton appear to believe, then Britain has an even greater responsibility to ensure that every pound spent on defence delivers the maximum possible strategic effect. 

Yet too often European defence procurement remains fragmented and inefficient. 

Perhaps the clearest example is Europe's approach to sixth-generation combat aircraft. At present, two separate programmes are being developed simultaneously: the UK-led Global Combat Air Programme (GCAP), involving Britain, Italy and Japan, and the Franco-German-Spanish Future Combat Air System (FCAS). 

Both projects have merit. Yet at a time when governments across Europe are searching for additional defence resources, it is legitimate to ask whether the continent can afford such duplication. 

The same challenge can be seen across missile systems, armoured vehicles, naval platforms and defence research. Europe collectively spends vast sums on defence, but often fails to generate the military capability that expenditure should deliver because investment remains dispersed across overlapping national programmes. 

That reality strengthens, rather than weakens, the case for closer UK-European cooperation. 

Britain should be leading efforts to deepen defence industrial collaboration, pursue joint procurement where appropriate, align future capability requirements and strengthen Europe's collective defence industrial base. Such cooperation would not diminish sovereignty; it would enhance our ability to act by ensuring that Europe possesses the industrial capacity, technological capability and military resilience needed to defend itself in a more uncertain world. 

The UK-EU Security and Defence Partnership agreed last year provides an important foundation. The next step must be to turn that political commitment into practical cooperation through joint capability development, industrial collaboration and coordinated investment. 

John Healey's resignation has highlighted an uncomfortable truth. Britain faces growing threats at a time when resources are under pressure and old assumptions about security are fading away. 

The response cannot simply be to ask how much more money can be found. We must also ask how Europe can make better use of the resources it already possesses. 

If the Defence Investment Plan is to succeed, it must recognise the reality of modern security. Britain's future security will depend not only on the strength of its own armed forces, but on the strength of the continent alongside which they operate. 

In an age of growing threats, finite resources and a changing transatlantic relationship, Britain needs a Defence Investment Plan that is truly continental in its ambition.