One of the things that is really difficult to get a grasp on is the reality surrounding the Druid society in the UK. Having hung out with many Wiccans in my day, I thought I had this part under control. Then I got to school and realized that a lot of what I knew was romanticized nonsense, so here to save the day is this book by Ronald Hutton.
I first came across Hutton while trying to sort out fact vs fiction as it pertained to agricultural holidays observed in the UK. I really appreciate his cut through all of the nonsense style. Although his documentation has forced me to re-evaluate a lot of researchers work, it is a good critical thinking exercise.
He has written several article/books that a SCAdian might find useful.
Hutton, Ronald. “How Pagan Were Medieval English Peasants?” Folklore 122, no. 3 (December 2011): 235–49. doi:10.1080/0015587X.2011.608262.
Hutton, Ronald. Blood and Mistletoe: The History of the Druids in Britain. New Haven, CT: Yale University Press, 2009.
Hutton, Ronald. Stations of the Sun: A History of the Ritual Year in Britain. Oxford, England: Oxford University Press, 1996.
Hutton, Ronald. The Pagan Religions of the Ancient British Isles: Their Nature and Legacy. Oxford, England: Blackwell Publishers, 1991.