British Coinage

• From 1660 to 1817 ( Charles II to George III )

  1 Guinea = 20 Shillings (20s) = 240 pennies (240d)
  1 Shilling (1s) = 12 pence (12d)

• From 1817 to 1971 ( George III to Elisabeth II )

  1 Pound (£1) = 20 Shillings (20s) = 240 pennies (240d)
  1 Shilling (1s) = 12 pence (12d)

Other denominations of predecimal British Coins

Guinea = 21 Shillings = 1 Pound + 1 Shilling
Soverign = 1 Pound
Crown = 5 Shillings
Florin = 2 Shillings
Groat = 4 pence
Farthing = ¼ penny

• From 1971 to date ( Elisabeth II ) Decimal Coinage

  1 Pound (£1) = 100 pennies (100p)

  Notes:
  The symbol, £, for the pound is derived from the first letter of the Latin word for pound, the librum.
  The old abbreviation for the penny, d, was derived from the Roman denarius, and the abbreviation for the shilling, s, from the Roman solidus. The shilling was also denoted by the slash symbol, also called a solidus for this reason.
  The English penny was derived from a silver coin (the sceat of 20 grains weight) which was in general circulation in Europe during the Middle Ages. The weight of this coin was originally 20 grains but was fixed at 22.5 grains by Offa of Mercia (an 8th century contemporary of Charlemagne), or 1/240 of a Tower pound-around 1.46 grams.
  The Troy pound replaced the Tower pound in the 16th century, but by then the penny had been heavily debased to about a third the silver content of a proper Troy 24 grain pennyweight (1.555g).