In fact UK car companies WERE soot covered factories (eg Jaguar and Land Rover) as recently as the 1990s (when Ford bought them and completely upgraded their production lines).

The UK going alone on military equipment:

  - loses out on comparative advantages
  - needs to make redundant capital outlays
  - loses allied buffer countries
  - can’t maintain their own nuclear weapons (the uranium wasn’t sourced from Wales, ya know…)
  - needs to spend MUCH more than the average NATO member country (military spending as a percentage of GDP)
  - it’s not like the UK government budgets are overflowing with surplus to spend.