Reddit reviews Betwixt & Between: Exploring the Faery Tradition of Witchcraft

There are a few books that deal with this. Apparently the myth comes from aboriginal people from Western Europe, who used to live in grass-covered houses, and were generally smaller, darker and more mischievous (?) than the rest of the population, and practised witchcraft.

I've read this in books about the history of Pagan witchcraft in England. That might be a good angle to search from.

Books in this section are likely to have a chapter on fearies (but I'd check), but it won't be fully about fearies; whereas this one might be more specific, but more from a practical viewpoint (I think they usually use the spelling "fearie" - for your future searches).

Edit: OH! Also, Witchcraft Today by Gerald Gardner (which is very worth a read anyway) has a section on "The Little People" - that's about fearie lore. :D