Under ever-increasing population pressures in their Scandinavian homelands, where flat, suitable farmland was scarce, they established settlements in coastal areas of England, Scotland and Ireland, where they founded Dublin in 841.

These sea-borne adventurers also established colonies on the islands of the Hebrides, Orkney and Shetland, and as far west as Iceland, Greenland and even north America.

 The Hebrides remained under Viking control until 1266, and Orkney and Shetland until the 15th century. A dialect of Old Norse was still being spoken in Orkney, where half of the modern population has been found to have traces of Viking DNA, as late as the 18th century.

Other groups of Scandinavian settlers founded the duchy of Normandy, from where came William the Conqueror in 1066. The name, Normandy, is derived from the description of the people who settled there: 'Norse men'.

In England, an invasion by the 'Great Army' of Vikings in 865 led to the destruction of all the old English kingdoms except Wessex.

It was only under the leadership of Alfred the Great that the tide of conquest was stemmed, but even he was forced officially to recognise their presence in 871. In 886, Alfred reached agreement with Guthrum, the Viking ruler of East Anglia, whereby the Vikings were acknowledged as rulers of the north-eastern half of England – the area that became known as the Danelaw.

Viking rule ended there in 954, when Eric Bloodaxe, the last Viking king of York, was deposed and killed.

 By then, though, there had been widespread Scandinavian settlement in north-eastern England – a fact reflected in place-names to this day – not least in important centres of population such as York. There must already have been a considerable confluence between Anglo-Saxon and Scandinavian ways of life, and the assimilation of the settlers under English rule accelerated following their conversion to Christianity.

In 1016, the king of Denmark, Cnut, reconquered England and held the throne until his death in 1035.

The ordinary person living in England at the time would probably have noticed little difference between his reign and that of the Anglo-Saxon kings who preceded him, although his better-off English subjects often lost their land to Danish incomers and he ruthlessly disposed of political rivals.

 His sons, Harold Harefoot and Harthacnut, couldn't hold his empire together and the throne of England reverted to Anglo-Saxon control until the Norman invasion in 1066.

Although their violent reputation may have been deserved, the Vikings were probably no worse than most other peoples in what was a very unstable and violent period in English history.

Indeed, the Anglo-Saxon occupation of England had taken place in much the same way as that of the Vikings – and the various Anglo-Saxon kingdoms that existed before the arrival of the Vikings were at almost constant war with each other.

The Vikings may even have reduced the level of violent conflict in England by destroying the other Anglo-Saxon contenders for pre-eminence and leaving only the kingdom of Wessex to eventually unite the country under one king.