I mean yes, that makes sense.

But, the issue is about capacity. Steel and metals generally are a core part of the UK economy. Yes we could just buy it all in from outside, but when geopoltics intervenes it leaves us high and dry (see natural gas, chemical production, wire making, transformer making, etc etc)

If we end up in a war, which seems fairly reasonable, then we need to have access to a manufacturing, not only prototypes, but large scale manufacturing. we need not only the machines, but the people, experience and pipelines to keep that working.