If you don't mind me asking, roughly where in the UK do you live? Almost everything I want grows in your area.
I have done most of the UK at most points during the year, and what I have not I have seen the weather for and during the not harvesting months. Does not matter really. Seaside you might get some more samphire (though at the same time one of my favourite walnut trees is not far from a spot I might get that in, and fruit trees are equally plentiful if you got vaguely inland) and go further north and start doing Scotland and you get some wild raspberries (they are rare as anything down south). Plums/bullaces and greengages take a bit of searching in general, and quinces something quite rare indeed (though there are wild varieties some might mistake for crab apples). More rural does better than dense urban but I have found stuff even in casual walking distance of City of London (as in the little bit in the middle near a lot of the tourist stuff), and older towns usually have quite a bit if you go looking (though it has been long enough since the post war town building bit that there is even a fair bit in "garden cities", just not so much of the really fun heritage stuff randomly growing on the edge of a field).
https://footpathmaps.com/
https://www.rowmaps.com/
Walk the fields and the older parts of any given location and you will find things. Tracks between villages and churches or schools (the grab a plum, eat it and chuck the stone 60m later might well have resulted in a line of plum trees, same for apples) are a good start. Can find even more if you go off the beaten track, or indeed actually stay on the track if the track is a road without a path (other week I had enough apples in my bag from the side of a local rat run road sort of near but not on a footpath that my shoulder was tired when I got back). Last night I came back with several bags of small pears from a fairly new (90s for most of it) estate in a small town.
If you want to ask people (box for you, box for me or something) if you see something in their garden then that also does many things for people (I have even been in places where someone had a magnificent herb garden, as in several types of mint for different occasions, and did not pick their fruit or did not want to climb a ladder to get it).
If you want to get better still (I did not mention elderberries, rosehips, sloes/blackthorn, if you are really fancy/bored hawthorn jelly is a thing, black and red currants, hazelnuts are a thing but squirrels usually get them, didn't touch on greens that all the rural kids would used to have known, wild garlic, nettles (nettle soup is wonderful), mushrooms are a thing if you want to take the time to get to know them*) then there is also that.
*don't get me wrong there are maybe 3 people I have ever met that I properly trust to pick mushrooms for me and know them. At the same time the edible ones are usually fairly obvious and while many will also have look a likes that at first glance might seem very similar then they do have telltale other signs. Or if you prefer the main taboo against eating them was because they used to been as reserved for the priestly class.
You have to occasionally adjust your tastes (granted I actually find supermarket apples too sweet these days), and adjust your prep (smaller things are harder to peel** and may have had insects get to them so prep accordingly). You might also end up with a glut of things so end up having to preserve them (my freezer right now has more apple sauce, juice, puree than I am likely to use in the next year, and that is not counting chutneys and pickled things).
**get a conical sieve, leave the skins on and adjust the recipe. Hopefully you already have a maslin pan. You are welcome.
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RedColoredStars:
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SylverReZ:
