The Ministry of Defence has poured cold water on Donald Trump’s grandiose £1 trillion ‘Golden Dome’ missile defence plan, warning that it would be ‘insufficient’ to protect the United States from a full-scale missile attack. For those who have followed the former president’s flair for hyperbolic branding, the name alone should have raised eyebrows. It evokes not military strategy but a luxury golf resort. And now the MoD’s analysis suggests the economics of this scheme are as shaky as its physics.

Let us be clear: missile defence is a seductive concept. It promises to shield a nation from the ultimate threat, to turn the sky into an impenetrable barrier. But the market has always been sceptical. The reason? The cost curve is steep, and the technology is inherently unreliable. Against a single rogue missile, systems like Patriot or THAAD have a respectable track record. But against a saturation attack of dozens or hundreds of warheads, the arithmetic quickly turns grim. Each interceptor is a high-precision weapon costing millions; a decoy can cost thousands. The defender must be right every time, the attacker only once.

Trump’s plan, reportedly modelled on Israel’s Iron Dome but scaled up to a continental level, would require thousands of interceptors, space-based sensors, and a network of radars that would dwarf any existing infrastructure. The £1tn price tag is eye-watering, even for a nation with a $30 trillion GDP. But the MoD’s concern is not just cost, it’s effectiveness. In their assessment, Golden Dome ‘may not be able to protect the US against a fully fledged missile attack from a near-peer adversary’. That is diplomatic language for: it’s a dud.

The parallels with financial folly are striking. This is a project that promises a return on investment that simply does not exist. The net present value of avoided nuclear annihilation is incalculable, but the probability of 100% success is zero. Markets abhor unbounded risk, and this plan is a case study in moral hazard: it invites the very attack it seeks to prevent by creating a false sense of security. The gilt-edged equivalent would be a sovereign bond that guarantees repayment in the event of a government default.

Central bankers have long warned about the dangers of ‘repression’ when states meddle with market mechanisms. Here, Trump is attempting to repress the laws of physics and probability. The MoD’s analysis is a cold splash of reality: a fully loaded attack, with multiple warheads and countermeasures, will bypass any defensive shield. It is a classic case of diminishing marginal returns. The first billion pounds buys a lot of protection; the next trillion buys very little.

Moreover, the political economy of Golden Dome is toxic. The US would be dependent on a single, government-run programme prone to cost overruns and delays. The private sector, which thrives in the aerospace defence industry, would be subordinated to public sector whims. We have seen this before in the NHS IT systems and the RAF Sentinel contracts. When the state becomes the monopoly buyer, efficiency evaporates. Capital flight follows; investors flee to more predictable environments.

Inflation is another worry. A £1tn injection into the defence sector would scramble supply chains, raise wages for engineers, and crowd out private investment. The Bank of England and the Federal Reserve would have to raise interest rates to curb the resulting demand-pull inflation. The consumer, already squeezed by rising prices, would bear the cost of this fiscal expansion without any near-term benefit.

Of course, defence is a public good, and the state has a role. But the MoD’s warning is a reminder that grand visions often crumble against the hard anvil of reality. Golden Dome may shine from a distance, but up close it is more fool’s gold than strategic asset. The prudent investor knows when to walk away from a bad deal. The MoD has effectively signalled that this one is not worth the premium.