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, British coins contained no silver.
From 1971-on, British decimal coins were issued and contained no silver.
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.
Prior to 1920
British silver coins contained high purity, 92.5% (Sterling) silver. These coins contain the following amounts of actual silver weight:
Three pence (.0420 Troy ounces of actual silver weight) 1.2 grams
Sixpence (.0841 Troy ounces) 2.4 grams
Shilling (.1682 Troy ounces) 4.9 grams
Florin (.3364 Troy ounces) 10.2 grams
Half Crown (.4206 Troy ounces) 13.0 grams
Double Florins (1887-1890) (.6727 Troy ounces) 20.7 grams
Crown (.8409 Troy ounces) 26.0 grams
All the silver weights above are for as-minted, uncirculated coins. Circulated coins will weigh somewhat less overall and thus have modestly less silver content than listed above.