The book seemed to be set between the wars and in hindsight felt like an English version of Huckleberry Finn. Three brothers decided to spend the summer in the woods near their house. I think two initially planned but ended up taking the youngest with them as well. They set up a small camp and salted a pig so they had food for the summer. They saw a night heron down by a river. They met an old man who lived in a house made from faggots, they were initially very scared of the old guy, but eventually saw him as no threat and made friends. He taught them how to smoke his pipe as they'd seen him smoking and were curious. I think they may also have lost some of their food to what they thought was a bear but ended up being a badger, that might have been a beehive that they came across.
I read the book in around 1985 but it was clearly written much earlier than this. I think it's called Bear Woods but I may have conflated that with a local area of the same name. The version I had was blue cloth no dustcover and had some beautiful white on black illustrations. Nobody I know as an adult has ever heard of it and maybe my google-fu is terrible but I've failed to find it anywhere online either. It's clearly a children's book, but not in the sense of a picture book with a few simple sentences. It's a coming of age story which I would love to revisit.