In the early 2000s, I heard an audiobook version of a coherent retelling of the classic Robin Hood story. There was a frame story set in the modern world, a boy (I think) staying with his grandmother (?) who survives a massive storm one night and, after picking some berries in the morning, finds a huge oak that's blown down and a skeleton underneath it.
Then the tale of Robin Hood begins, starting from his childhood with his father (Martin?) and going through his whole life. He meets Marian as one of the "woodland folk" (some kind of exiles?) and they later have a son who's also called Martin after his grandfather. As well as the usual antagonist of the Sheriff of Nottingham, there's a woman referred to as "the abbess": I remember a line from Friar Tuck "I may be a sinner, but [the abbess is pure evil]". After many years, at the end of the story when Robin Hood is old or sick (?) and seeks shelter at a nunnery, the abbess crops up and poisons him to death with belladonna (deadly nightshade). His friends bury him with his longbow and an acorn - we're meant to surmise that the same acorn grew into the mighty oak that's just blown down hundreds of years later.
Back in the frame story, the boy goes home to his grandmother with the berries he picked, which turn out to be belladonna as well. Luckily he hadn't eaten any, but it provides a thematic connection between the main story from the past and the frame story. I don't know if it's implied that the boy in the modern world is Robin Hood reborn, or if it's left to the reader's imagination to make any explicit connection.
Obviously the setting is England; I got the audiobook from a public library in England; and probably the author is also English.
What was this story? It's always stuck in my mind, much like this Iliad retelling, but I don't remember the author.