After his first expedition to England, Sweyn was resorted to extracting payment by blackmail as opposed to ravaging English shores. King Ethelred II the Redeless, the weak and ineffectual King of England, had ordered a general massacre of Danes in England on St. Brices Day, 1002, which included men, women and children, none were spared from the savage slaughter. Sweyn swore on the bragging cup to be avenged on Ethelred and landed in England, at Sandwich in 1003, ravaging much of the south of the country, he then proceeded to the Humber, Northumbria surrendered to him, he then proceeded to Winchester and on to London. The Londoners put up a stout resistance, King Ethelred and Thorkell the Tall, a Viking leader who had defected to him, were in the city. Sweyn then proceeded west to Bath, where the western thanes submitted to him. The Londoners fearing an awful revenge would be exacted on them if they resisted any further, followed their example and at last submitted.
Ethelred fled to the Isle of Wight and later joined his wife and children in Normandy, where they had taken refuge with her nephew, Duke Richard. Sweyn was declared King on Christmas Day, 1013. Some of the English provinces refused to pay homage to the Dane, who had no dynastic right and claimed the throne by right of conquest. He was never crowned.