The English penny first appeared
in Anglo-Saxon times, as a silver coin. It was derived from another
silver coin, the sceat, of 20 troy grains weight, which was in
general circulation in Europe during the Middle Ages.
The weight of the English penny was fixed
at 22.5 troy grains (about 1.46 grams) by Offa of Mercia, an 8th
century contemporary of Charlemagne.
The coin's designated value, however, was
that of 24 troy grains of silver (one pennyweight, or 1?240 of
a troy pound, or about 1.56 grams), with the difference being a
premium attached by virtue of the minting into coins.
Thus 240 pennyweights made one troy pound
of silver in weight, and the monetary value of 240 pennies also became known as
a "pound". (240 actual pennies, however, weighed only 5400 troy
grains, known as tower pound, a unit used only by mints. The tower pound
was abolished in the 16th century.) The silver penny remained the primary unit
of coinage for about 500 years.
The purity of 92.5% silver (i.e., sterling
silver) was instituted by Henry II in 1158 with the "Tealby
Penny" — a hammered coin.
Over the years, the penny was gradually
debased until by the 16th century it contained about a third the silver content
of a proper troy 24 grain pennyweight.
By 1915, a penny was worth around 1/6 what
it had been worth during the Middle Ages. British government sources suggest
that prices have risen over 61-fold since 1914, so a mediaeval sterling silver
penny might have had purchasing power equivalent to £4.50 today, and a farthing
(a quarter penny) would have the value of slightly more than today's pound
(about £1.125).
