I disagree Roger, the sovereigns do have a standard legal tender value of one pound, but no one would sell them at that price because the gold content value is much higher. Sovereigns circulated as legal tender coins for over a century. That is the modern sovereign and does not count the hammered sovereigns which are much older. Just because a coin does not state a denomination on them, does not make them a token or bullion coin. Sovereigns became bullion in England circa 1917 when they were not released for circulation any longer and were used strictly to pay war debts. They did still circulate outside England for some years after England stopped producing them for circulation. Sovereigns were also legal tender in Portugal even though Portugal was not part of the British empire. The world accepted the sovereign as circulated legal tender coins and later as bullion.
The below book, is an excellent first read on the subject. Many others out here as well: