> I've no doubt that a sudden cataclysmic change to international trade would spike food prices and increase poverty-derived food insecurity. But I doubt there would be physical calorie shortages.

If there was a sudden change, there might be calorie shortages. However, I agree that if importing become more expensive over the longer run, or even if there was a quick change, but one that could be predicted years in advance, there would be no calorie shortages.

However, the same is true for lithium: the UK could mine its own lithium, if importing become infeasible. I am not sure though, if it would make commercial sense even then: you can make batteries (and other gadgets) without lithium, and for many applications you can make do without batteries at all.

Eg instead of solely driving electric cars with home-grown lithium batteries, on the margin I would expect more people to take the train.