The Mistake: Chopping a Neighbor's Overhanging Tree and Keeping the Wood
You are legally allowed to trim a neighbor's tree branches if they overhang your property, but if you keep or dispose of the wood, it is technically theft.
Boundary disputes over large trees are a classic British neighborhood argument. If a neighbor's tree branches grow across the boundary line into your airspace, you have the common law right to cut them back to the boundary line without asking their permission.
However, the misunderstanding is what you do next. The branches—and any fruit on them—still legally belong to your neighbor. If you chop off the branches and throw them in your own green bin, or throw the neighbor's apples in the compost, you have technically stolen their property. You must carefully offer the severed branches back to them (though you cannot simply violently chuck them over the fence, which could be classed as fly-tipping).