Imagine a situation in which, for thirty-five years, the English experienced unprecedented levels of engagement with Continental Europe. In consequence, they came to enjoy greater prosperity than they had known at any time since the fall of Rome. Then followed a period of uncertainty. Failures of government led to a break with England’s allies and a sudden withdrawal of the English from the Continent. An economic downturn ensued, accompanied by rising xenophobia, leading almost immediately to the greatest constitutional crisis in English history.

If the circumstances outlined here seem familiar, then they just as easily apply to the later 12th century as to more recent events. Between 1154 and 1189, Henry II of England assembled the greatest collection of lands of any western king since Charlemagne. Born the son of a mere count of Anjou, via his mother (the daughter of King Henry I of England) and his wife (Eleanor, heiress to the duchy of Aquitaine), Henry came not only to wear a royal crown but also to outmanoeuvre all his European rivals. Through a combination of military and political skill, his lieutenants came to rule in Brittany, Dublin and, rather less securely, Edinburgh. Paris itself became a French frontier town, walled and fortified against the threat of English conquest. By the 1180s, Henry’s children had married into the ruling dynasties of Germany, France, Spain and Sicily. Such was his power that even the keys of the city of Jerusalem were offered to him as a token of his greatness.

Henry’s achievements were all the more remarkable given that, in the eyes of many, his origins were satanic. According to family legend, itself keenly promoted by Henry and his sons, his was the ‘Devil’s Brood’: descended from the she-demon Melusine, half-woman, half-serpent. ‘From the Devil he came, and