I don't buy that. Any evidence other than the Wicker Man out of the White Goddess out of the Golden Bough? I'm not saying that kings or chieftains were never sacrificed, but what evidence is there that any of the bog bodies were kings? They were high status, certainly. If a king went as a willing sacrifice, would he have been tortured and de-nippled? Tacitus tells us of ritual sacrifice and of criminal or breach of honour executions. I'll go with him rather than romantics like Fraser and Graves.