I would be interested in any links you might have access to. I have no doubt our ancestors were barbarians in the past. I know some things about the Vikings, who were really savage, but not as much about the English, except from the movies “Brave Heart” ,”The Patriot” and “Rob Roy”.
Prehistory is a bit light but he does a great job of covering the subject.
"Pagan Celtic Britain" by Anne Ross is another good one on their religious practices.
The Celtic practice of human sacrifice shocked even the Romans who were no slouches themselves when it came to killing people to win the god favor.
There are only a handful of pre-christian groups that quit human sacrifice. Egypt, Persia, Israel and, oddly enough, most North American Indian tribes.