This large share of power, thus conferred by the people, though intended to preserve the liberty of the subject, was perhaps unreasonably detrimental to the prerogative of the crown: and accordingly we find a very ill use made of it by Edric duke of Mercia, in the reign of king Edmond Ironside; who, by his office of duke or heretoch, was entitled to a large command in the king's army, and by his repeated treacheries at last transferred the crown to Canute the Dane.
Source: wiktionary