What this song renders
The waiting is documented. After Cnut died in November 1035, a council at Oxford left Harold Harefoot as regent and Emma at Winchester “with the housecarls of her son,” holding Wessex for Harthacnut. He did not come: Denmark was under threat from Magnus of Norway, and he most likely stayed to defend it. Harold’s men took the best of the royal treasure from her, and in 1037, in the Chronicle’s words, Harold was chosen king everywhere “and Harthacnut was forsaken because he was too long in Denmark.”
The cost fell on her. The same year she was “driven out without any mercy to face the raging winter” and crossed to Bruges, where Count Baldwin of Flanders took her in. Harthacnut came in the end — in June 1040, after Harold’s death, with sixty-two warships — four years after she had been told to hold Winchester for him.
The song’s middle is staged. The erosion of support is the Chronicle’s; the thegn, then his brother, then his men, is the song’s way of showing it. The Itchen is Winchester’s river and navigable from Southampton Water, so a sail coming up it is period-correct — but the ship carrying Harold’s letter, and the tide over her shoes, are invention.
Emma holding Wessex for Harthacnut, his staying in Denmark, the loss of support, Harold’s accession in 1037 and her expulsion to Bruges are documented. The deserting thegns are a dramatisation of a recorded collapse; the wrong ship, Harold’s letter and the tide are the song’s staging.