In 1997 to mark the 10th Anniversary of the introduction of the Gold Britannia Coins the Royal Mint released a very Limited Issue Britannia 20p Twenty Pence Silver Proof Coin struck in solid .958 Silver weighing one tenth of an ounce of pure Silver to commemorate the tercentenary of the introduction of the Britannia Silver Hallmarking Standard.
The Britannia Silver Standard was first introduced 300 years ago to protect coins of the Realm, produced in sterling (.925) silver, from being melted down into plate. To discourage the practice, a Statute was passed raising the standard for wrought plate to .958 silver. Appropriately, the hallmark, attesting to the fine silver content, is the recognisable seated figure of Britannia.