The UK's call to "buy British by default" has a wartime air, yet makes little sense for actual defence equipment. National defence contractors rely on hundreds of small and medium-sized suppliers spread across the world, including giants like BAE Systems and Lockheed Martin. Smaller manufacturers of high-tech equipment too have planet-spanning supply chains.

Moreover, even domestic companies are often funded with overseas money, especially start-ups relying on venture capital. Berlin-based Stark, recipient of a recent contract to supply Kamikaze drones to Germany's military, is backed by US tech entrepreneur Peter Thiel. A big problem with nurturing national champions is that similar companies in different countries end up duplicating each other's labour and becoming reliant on single government customers, who can prove fickle.

If governments really want to keep defence procurement close, teaming up with allies is the solution. Successful models include European missile manufacturer MBDA, co-owned by BAE, Airbus, and Leonardo, which increased sales by 17 per cent last year. German munitions maker Rheinmetall has signed up 21 joint ventures and partnerships since late 2023 to access capacity, technology, and capital.

For companies and governments, cross-country collaboration is a way to parlay each other's strengths and hedge risk. The UK's record in delivering defence ambitions has been patchy, with all but two of the country's 49 recent major projects delayed or over budget. Joining forces with like-minded allies feels like a smarter way ahead.