Badenoch's £10bn air defence plan points to growing concern over protecting UK's skies

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.