I do prefer British produce especially livestock products for welfare reasons but there isn't enough of it to feed everyone in Britain . At present if you look on the supermarket shelves you will see that most food comes from Denmark, France, Spain and even further afield, Africa, New Zealand and South America.
My point is that with Brexit we will have to import livestock produce from the US instead of the more expensive food from Europe. We already know that the cheaper US meat and dairy is not as pure as the European equivalent. Most people. me included, cannot afford to buy more expensive food.
Brexit and worse, global warming, will make food more expensive sooner or later.
I do know about the Yorkshire vinyard, and that is one of the hot summer's great successes.