(Author's Note: Ireland was left almost entirely off this list because it's not part of Britain. Northern Ireland was left off due to the controversial nature of its status within the British Isles.)
The Ancient British Practiced Cannibalism
Artifacts found in a cave in Somerset, England, suggest that the people of prehistoric England were big-time cannibals. Human remains with bite marks, and carefully sculpted human skulls that look like bowls, suggest that the people of this area were eating their own dead. The practice seems to have been primarily practical—why let good meat go to waste? Primitive stone knives were used to carve meat and muscle from bodies, while bite marks were found on ribs and even toes.
Humans Were Murdered in Brutal Sacrifices
Well-preserved bodies found in bogs suggest human sacrifice in pre-Roman Britain. These bodies exhibit brutal wounds: one was hit so hard in the back of the head, skull fragments went into his brain and his teeth broke; his throat was then slit. Roman writings also attest to human sacrifice, though beyond descriptions of the physical killings, its unclear whether the Romans actually knew what they were talking about.
"The Wicker Man" Is Real
Druids performed all manner of rituals in Britain, including, according to Roman sources, human sacrifice. One form of druidic human sacrifice entailed building a large, hollow man out of wicker, filling it with human tributes, and then lighting it on fire. Some scholars suggest Romans made up the part about the wicker man containing human sacrifices (seriously, wouldn't a giant structure made of wicker just collapse if filled with the weight of human bodies?) —the druids simply burned an effigy of a man as an offering to gods.
The Oldest Human Remains In Britain Are of a Young Shaman Covered in Red Paint
The Red Lady of Paviland (actually the remains of a young man covered in red ochre body paint, who was probably in his 20s when he died) are the oldest human remains yet found in Britain, at 34,000 years old. The Red Lady was buried along with various artifacts in a cave in Gower, Wales; the nature of the burial makes the site the oldest ceremonial burial ground in Western Europe. No one is sure who the Red Lady was, but many speculate he may have been a shaman or mystic.