Just a thought, and a bit of a wild one at that:

I mentioned Worm Hill to a friend whose been there. They were keen to point out that they'd not spent much time there, but they had wondered if the whole hill was artificial. They said it wasn't a very tall or large hill - in fact, they said its size reminded them of the Thornborough Henges. Anyway, when I look at it on the map it strikes me as somehow odd that it should be so close to the river. Wouldn't erosion mean that there shouldn't be a hill there?

Please tell me I'm talking crap if that's the case! ;) I thought it worth at least mentioning, though.