When first minted, in the reign of Henry VII, it had a value in exchange of twenty-two shillings and sixpence. This fell in subsequent years, but was legally fixed at twenty shillings in 1817. It ceased to be circulated in 1914, even though sovereigns and half-sovereigns continued to be minted until 1975. Their disappearance is understandable, for commercial if for no other reasons, as the intrinsic value of the sovereign is now far greater than its face value and its market value considerably higher again. Half-sovereigns, which are more difficult to obtain than full sovereigns, may have a greater market value than the latter.
Reference: The Penguin Business Dictionary, 3rd edt.