For those of you who wondered about the consultant historian who worked on the film: John Matthews, along with his wife, is an "an internationally renowned authority on mythology and folklore with a special interest in the Arthurian and Grail traditions and Celtic lore. A professional writer since 1980, he has produced over forty books ranging from the worlds of the Celtic and Arthurian legends to collections of stories, essays, and poetry. His first-hand experience of native shamanism and druidism grounds his work in a practical and traditional foundation, making his books both communicative and exciting. He has given highly acclaimed workshops in Britain, Central Europe, and America. He is primarily concerned with the interpretation of myth as the key that will open the door to the lost sacred dimension of the world." (Bio quoted from questbooks.net.)
The current news page on his own website describes what he's currently working on, if you're interested in more information.