If we couldn’t import, we would survive.
All 62 million of us?
You export as much as you import so your statement makes no sense.
Of course it does. We export skills and material goods. Food is quite different. We do not export 40% of our required food.
There is a hell of a lot of military land in the SE doing nothing.
We could put a lot more sheep in Wales etc.
Dig for Victory and all that.
In other words, no, not without a massive change to our living conditions.
In short, if there was a short notice catastrophe (sudden oil stop for instance), a large percentage of our population would die off.
Those that say “we would adapt” are quite right. Given enough warning, we could prepare for such an eventuality, and could feed ourselves. However, a short notice upset would kill off a large portion of the UK without outside aid.