It is easy to forget that defence and security are not the same thing. Defence is what countries must resort to when their security breaks down. And during peacetime, countries spend money on defence precisely because they fear for their security.

Since 2014, the security environment for Britain and the European Union has deteriorated sharply. In March of that year, Russia invaded Ukraine and annexed Crimea. It was the first time since World War II that a major European power sought to redraw its own borders by force of arms.