MODERN HISTORY OF UK COIN COMPOSITION
The standard circulating denominations of pre-decimal British coins from 1800 to 1946, which contained 92.5% or 50% silver, included threepences, sixpences, shillings, florins, two shillings, half-crowns, double florins, and crowns.
In 1920, the silver content of all British coins was reduced from 92.5% to 50%, with some of the remainder consisting of manganese, which caused the coins to tarnish to a very dark colour after they had been in circulation for a while.
Silver was eliminated altogether in 1947, except for Maundy coinage, which returned to the pre-1920 92.5% silver composition.
There have been four distinct eras of British coins since 1800:
Prior to 1920, British silver coins contained high purity, 92.5% (Sterling) silver.
From 1920 to 1946, British silver coins contained 50% silver.
From 1947 to 1971, some denominations of British pre-decimal coins issued for circulation were “silver-colored,” however these coins were made of copper-nickel, and contained no silver.
From 1971-on, some denominations of British decimal coins issued for circulation were “silver-colored,” however these coins were made of copper-nickel, and contained no silver. In addition, there have been some silver decimal coins minted in limited quantities as commemorative or bullion issues, typically in Proof condition; these coins were not intended for circulation.