Currently the country has a number of systems to deal with short and medium-range threats – from drones to cruise missiles. But the armed forces still lack a weapons system to deal with long-range ballistic and hypersonic missiles.
And those don't come cheap. Each interceptor used by the US Patriot missile system costs about $4m (£3m).
Sophisticated air defences that can deal with a range of threats are expensive. The US Army alone wants to increase its budget for both missiles and interceptors by fourfold next year – to $36bn (£27.1bn).
Israel also spends a significant proportion of its $45bn (£33.9bn) annual military budget on air defences.
For the Conservatives there's also a presentation problem. Their original press release mentioned building a new air defence systems that would be "in essence, a British Iron Dome", referencing Israel's elaborate air defence system.
But any comparison of the challenge of defending Britain's skies with Israel's, about 10% the size of the UK, is naive.
Nor is the threat the same. Israel has regularly been targeted by drones and missiles over the past decade. The UK has not.
The Conservatives now suggest the phrase "Iron Dome" was just a shorthand for better air defences. But even the words "Britannia Shield" may be a misnomer.
It would be nigh on impossible for the UK to develop an air-defence system that could defend the whole country with such limited resources.
At best it could afford a system to protect some key strategic sites – including military bases. At present the UK doesn't even have that.
By BBC Verify
Nick Forienza, a defence analyst from Janes, a military think tank, said the money committed by the government to missile defence under the Defence Investment Plan "is only a fraction of what other countries have declared".
He said the Conservatives' plan to invest £10bn "sounds comparable to what other small countries are doing".
He continued: "Not as small as the Netherlands or Belgium, but let's say Germany or Turkey and now the Greeks are working on something called Achilles Shield.
"That's the kind of magnitude [spending £10bn] that would be required for a serious missile defence system."
Germany is leading the European Sky Shield Initiative (ESSI), a 24‑nation effort to jointly procure air and missile defence systems (IRIS‑T, Patriot, Arrow 3).
Berlin has committed roughly €4bn (£3.4bn) for Arrow 3 alone and is also part of a €5.1bn (£4.3bn) plan to share up to 1,000 Patriot GEM‑T interceptors with Romania, Spain and the Netherlands.
In France, budgets show an "Air and Air Defence" spend of about €4.4bn (£3.7bn) in 2026, but this covers all air force air defence activities, not just missile defence.
Poland, which spends more on defence as a share of its economy than the UK, is building an air and missile defence system worth more than PLN 200bn (£39bn) which will be spent over a number of years.
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