It was my impression that the Vikings ruled in England for several generations. For instance Cnut was a major English king in the early 11th century.
The Vikings had a great deal of influence on English Law through the manorial court system and the underlying concepts of tort under notions of “trespass”
Viking laws were framed in terms of “injuries” to the rights of others, valued as:
Physical rights of “were” (life or limb);
Psychological status rights of “mund” (peace or privacy); and
Ownership rights of private property.
Trial and judgement were rendered by a tribunal of chiefs or an manorial assembly - the predecessor of the jury. Each injury was compensable through the award of monetary damages determined by the social rank of the parties and the severity of the injury.
Over a period of about twenty years, Svein and his son Knut (the latter for nineteen) ruled England, but not without having to fight continually. Knut must have been a warlike, bloodthirsty bastard, but he was apparently a pretty good politician, unafraid to delegate. Various Viking groups also occupied and ruled the Shetlands, the Orkneys (the latter also had been occupied by the Romans a thousand years earlier), many of the islands off the Scottish coast, and carved realms out of Ireland, over a period of centuries, finally getting broken at the last battle by Irish king Brian Boru. After William I conquered England (he was descended from Hrolf the Ganger, who had carved his realm of Normandy out of France), the House of Normandy and the succeeding Plantagenets started the British conquest of Ireland, which went on into the reign of Eliz I (at least). :’)
Speaking of which, that reminds me, I noticed a new bio of John of Gaunt the other day...