Must say it annoys me that except for shiitake, Asda never has UK grown mushrooms - all from Poland or Ireland. I buy mine elsewhere.
I do buy home-grown as far as possible - was pleased the other day to find lovely fat black English cherries - 750g for a fiver in M&S - and UK grown sugar snap peas in Asda.
Exceptions are obv. citrus and bananas, not that I buy bananas very often - and celery, which I do use a lot all year, so it often comes from Spain in winter.
Dh is addicted to strawberries on his muesli every morning, but he knows he'll get a rocket from me if he buys non British ones out of season - the season is now so much longer anyway.
Out of season he will often make do with stewed apple - made from the masses of windfalls in dd's garden. She hardly ever has time to do anything with them.
I never buy any non U.K. meat or bacon, though that's as much to do with animal welfare concerns as anything else..