80 pounds to buy food every mont?? Thats a lot of food you could by. No bother hunt or gather maybe?
In summer we live off the land, eat mostly fish & game. But I know no one up here who lives entirely on own caught food much anymore. We too like tea, coffee, sugar and vegetables and or fruit somewhat. On long trips we take store coffee, tea, flour, sugar and dried berries - you can buy them from your stores (raisins??) We make all we need from that. Bannock bread, bread with fruit, and so on. In winter we get most of the meat and fish we need from what we took in summer as we driy or smoke our meat and fish.
We can make labrador tea also out of snowberry which I've seen in the UK and also hemlockspruce, leaves, rasberry twigs and cherry twigs, which I also see in England. You must know these and more in the Uk and how to keep them all year. This is more important than finding place and where they grow.
Do you know much about food in the wild in UK? you have birch so you could collect sap. But do you know how to make sap into sugar to keep?
We have Bulrush, Aspen and basswood which I think I saw in UK my friend called it Lime tree. You get sap from and can eat leaves. Bullrush and Lilly have nice roots make good eating.
Up here another two months and we have first snow then freeze. You have much longer but time to prepare your food to keep you going is little time to do it. These things we must think about carefully be fore we go on long trips or stay in place we don't know very well.
My concern for your endevour is there isn't too much space in England to roam free and look and find best places to obtain sustinance as it appears all your land is private. I guess you can't shoot cattle, sheep & horses eh? And much of the land is given over to farms so no chance of finding wild food there. Mayb your police come looking?
We wish you well on your journey and hope you tell us how you are getting on.