countries were not invented in the era of the 1970's+
people actually can grow their own local veg of food groups that a re suitable for that area, and eat them
its the abundance of choice people want that makes people in the UK for instance want to get thai dragon fruit.
thai dragon fruit and asparagus is not a basic/crutial dietary need for brits. its a luxury/lifestyle food.
the issue is not need but ability and choice of variety.
if people want a car. UK can create all the cars needed. but some dont want just a basic car, some want styleish cars. some want glamourous cars.
functionally countries can survive on their own.
The UK can and right now proving they can make their own ventilators when the NEED arises.
the problem is that being able to get it elsewhere makes it less of a NEED to be self sustainable
..
we are not reliant on other countries. so we are not slave to china. but luxury consumerism just makes people want things from different places.. its a 'want' not an 'need' problem