The hallmarking system began in London in the year 1238 under the reign of King Henry III, when he ordered that all silver should be of the Sterling standard, that is it should contain not less than 925 parts per 1000 or 92.5% pure silver.
In the year 1697 this minimum standard was raised compulsorily from 925 to 958 parts per 1000 or 95.8% pure silver in order to stop silversmiths from melting coins of the realm for their raw material. This practice had become prevalent due to the shortage and high price of silver at the time.
To denote this new standard the Sterling lion mark was replaced by the figure of Britannia. However, the lower Sterling mark was restored in 1720 together with the lion mark, but the higher standard with the Britannia mark continues to this day.
Britannia standard silver is softer than Sterling therefore greater detail can be achieved when working it. Due to the higher silver content it also has a better colour than Sterling, the cost is proportionately higher as well.
In January 2000 in order to comply with European law, the fineness of all UK hallmarked articles must be expressed millessimally in parts per 1000.
There are four allowed in UK hallmarking
800 or 80% silver (often called continental silver)
925 or 92.5% silver (sterling)
958 or 95.8% silver (britannia)
999 or 99.9% silver (finest silver)