The British Crown coin, the successor to the English Crown and the Scottish Dollar, came into being with the Union of the kingdoms of England and Scotland in 1707. As with the English coin, its value was five shillings, or sixty pence - one shilling being twelve pence.
Crown coins issued during the reign of King George III are part of the great recoinage of 1816, and are the first issued for the United Kingdom (earlier, it was Great Britain). Unlike the other silver denominations of the time, they feature designs by Benedetto Pistrucci on both sides - an adaptation of the Saint George and the Dragon reverse from the first sovereign, and a laureate portrait of the king. Following the tradition of the time, the value of the coin is not inscribed on it - people were supposed to recognise it by its size and weight.
At the time the coins were issued, King George III no longer ruled in person but was subject to the regency of his son the Prince of Wales, later King George IV.
The composition of the coins is Sterling Silver (0.925 silver) and the coins have 0.841 oz ASW (ounces of Absolute Silver Weight); the standard weight for them was, in the measuring units of the time, 10/11 of a troy pound (436.3636 grains).
After decimalisation in 1971, the face value of the denomination kept its five shillings equivalent at 25 new pence, later simply 25 pence. Even though they have been withdrawn from circulation, pieces struck prior to 1990 - all the way back to 1818 - continue to be legal tender for that amount (i.e. they have not been formally demonetised). | 
