America has Miss Liberty. France has Marianne. In the UK it is Britannia who personifies integrity, honor, and beauty. She always wears a helmet and bears a shield and trident. These bullion coins are called 'Silver Britannias' and they pair up with 'Gold Britannias' as described on this CoinQuest page [Press Here].
There is an excellent summary of these coins over at Chards, specifically on this page [Press Here].
Since these are modern bullion coins, they trade at the current value of silver. You can look up this value at web sites such as kitco.com [Press Here]. At the moment, silver is trading at $15 US dollars per troy ounce, but tomorrow it will be different. Be sure to look it up. When you buy these coins they sell for more than silver value. When you sell them, they are bought for less than silver value. The margins depend on the size of the transaction. For a single coin, the margins can reach 50 percent or more, but for a single transaction of many coins, the margins can go down to 10 percent or less.