Allira
I look for them, especially now the British asparagus is in.
I bought a couple of kilos of asparagus from a farm in Norfolk yesterday, so I hope it's British (almost certainly not cut by British farm workers ... hmmm).
I grow my own rhubarb, beans and salad leaves and pick blackberries, blackcurrants, raspberries, gooseberries and blueberries myself (to freeze), so I know they're British. Friends give me apples, pears and plums (and even some cherries sometimes).
My meat (even chicken) is always British. I don't need a flag on any of it.
We're lucky we can grow so much, especially if people are prepared to eat crops in season.