Et "penny" a la même origine que le français "denier", raison pour laquelle (sur les timbres par exemple) dans certains cas il est représenté par l'initiale D ... et dans d'autres cas par P, parce que sinon ce serait trop simple !
"When dealing with British or Irish (pound) money, amounts of the decimal "new pence" less than £1 may be suffixed with "p", as in 2p, 5p, 26p, 72p. Pre-1971 amounts of less than 1/- (one shilling) were denoted with a "d" which derived from the term "denarius", as in 2d, 6d, 10d.
Irish pound decimal coinage only used "p" to designate units (possibly as this sufficed for both the English word "pence", and Irish form "pingin")." http://en.wikipedia.org/wiki/Penny