This theory has a lot of hate. It basically states that the English language became exchanged for a regional variant of Danish (compare Faroese to Norwegian), in much the same way that Frankish was for French or Gallo-Roman. I admit that the idea seems radical, but if the French are Franks, then why not speak Dutch or Franconian, but if not, then why not identify as Gauls how the Bretons call them? Similarly, the relationship between the English Folk and the Anglo-Saxon tongue was not static either and it may be the case that only Frisian is a true heir to the tongue once shared by both. Beowulf became the stimulating basis of this shift, because this saga is as English as Hengist and Horsa, mythologizing the English homeland, from whence the Danes followed. This same epic world included Hamlet and Macbeth.

From what is known of the Ingaevonic homeland, present-day Jutish is a form of Danish (just as Saxon became a form of Low German) and to suggest that is the case for those of Kent (home to the Church of England), ought not be strange. Angles come from South of Jutland, but North of the Danevirke, the traditional boundary with Saxony and Germany where Schleswig-Holstein replaced Hedeby. The embankments were in response to Frankish expansionism, echoed by legal jurisdictional partition of England at Watling Street, with the Danes on one side and the Saxons on the other. Saxons in Germany became a satellite folk of the French on one hand, while those in England intermarried with the French, while annexing the Jutish Kingdom of Kent in a comparable fashion to what would become of Jutland when Prussia invaded Denmark.

So, even if Alfred the Great had the Mercian Angles and Kentish Jutes under his rule, the Danes followed their kin to England just as they had to Jutland before. If it can happen once, why not twice? Not only were Angles, Jutes and Danes the basis of rule by Cnut the Great, but also the Norwegians, as he was King of Norway (the rightful native king was martyred) commanding Erik the Jarl of Lade who he made Jarl of Northumbria; but also the disputed King of Sweden (the rightful king went in hiding) and Svealanders followed him to England, where Thorkell the Tall was made Jarl of East Anglia.

It can be said that two parallel societies survived until Emma of Normandy's kin took the government away from both of them. In the time of Alfred and even Cnut, the West Saxon capital of Winchester was the capital of England, but while this changed under the Saxon heir Edward the Confessor to Westminster and might be seen as due to Norman interests, his half-brother Hardicnut who predeceased him, had the same Norman mother despite a Danish father. It's more likely that the increased population of the Danelaw had shifted the national focus toward the North Sea and not so much the Channel.

By the time Middle English was committed to paper, most of the Norman Lords had come to understand the forms of English spoken in Mercia and Northumbria, rather than Wessex, because the new middle class during the Teutonic Crusades and the Black Death had economic roots in the Eastern shires: Wat Tyler, Robert Kett, Thomas Wyatt, Wolsey, Cranmer, both branches of Cromwells, Walpole, etc. Non-rhotic Received Pronunciation comes from the Eastern shires. The Eastern shires are where the ancient textile industry has always been, due to Flanders of course, but the Hanseatic League tied England to the Baltic. This was the time of Wycliffe and Chaucer, 100 Years' War and Wars of the Roses.

It was only upon the colonial period, with the printing press and the Spanish Armada, that English came to integrate the Norman language and this is the stuff of Modern (British) English: King James Bible and Shakespeare. Republicanism came to the fore: whereas the War with France repudiated Normandy, overthrowing the Stewarts was a fulfillment of the Peasants' Revolt and broke the power of Normans in England--cut off from France. It is thus ironic that their tongue would become accessible to the Commons after deposing them in favor of Orange-Nassau, Oldenborg and Hannover, on the same level as the Saxon and Danish tongues of these newer dynasties already amalgmated due to the Saxons' and Danes' own sufferings under oppression long ago in England.

The three basic divisions of West Germanic:
Ingaevonic Frisian (inc. Old English--now Nordic)
Istvaeonic Dutch (inc. Old Frankish--now Romance)
Irminonic German

This explains how the differences between Ingaevones and Istvaeones became irreparable. Alfred the Great united the Angles and Saxons, who joined their Jute brethren in association with the Danes and then England became the future basis of the North's Kalmar Union under Saxon leadership, when Cnut the Great governed Scandinavia from his Danelaw foundations in England, with the end result of Norman rule being eternal war with the French. Merovingian Franks became fused with the Holy Roman Empire, both ruling it as Carolingians and assimilated by it under the Capetians. They insisted on being Romanized and Romanizing their fellow Germanic folks, but only succeeded in alienation between themselves and others, despite and to spite the lasting hegemony established by them. Only Irminones remained wholly West Germanic and that explains the rise of Germany as its own power distinct from both Scandinavia and Rome.