When Edward I hanged Jewish merchants for coin clipping in 1277, confiscating their goods and disinheriting their children, he was making a comment not only on the state of his own treasury, but on the economics of medieval life. Over the previous centuries, coinage–having been scarce once the Romans left Britain–had become more and more important in trade throughout England.

Edward the Elder (c. 902-925 AD) ordered: “there be one money over all the king’s dominion, and that no man mint except within port. And if the moneyer be guilty, let the hand be struck off with which he wrought that odense, and be set up on the money-smithy; but if it be an accusation, and he is willing to clear himself, then let him go to the hotiron, and clear the hand therewith with which he is charged to have wrought that fraud. And if at the ordeal he should be guilty, let the like be done as is here before ordained.”

William of Malmsbury wrote in 1140 AD: “Dearth of provisions, too, increased by degrees, and the scarcity of good money was so great, from its being counterfeited, that, sometimes out of ten or more shillings, hardly a dozen pence would be received. The king himself was reported to have ordered the weight of the penny, as established in King Henry’s time, to be reduced, because, having exhausted the vast treasures of his predecessor, he was unable to provide for the expense of so many soldiers. All things, then, became venal in England; and churches and abbeys were no longer secretly, but even publicly exposed to sale.” http://www.fordham.edu/halsall/source/1240stephen-badmoney.html

The small silver penny (pfennig) or denarius was the most common coin throughout the Middle Ages. The pound, which was 20 shillings, and a shilling, which was 12 pence, also was in circulation. The English kings began to mint a larger silver penny, known as a groat (big), beginning in the 13th century. It was worth four of the smaller pennies. All coins were made of silver until 1252, when gold coins (florins) began to be produced in Florence. The use of silver was soon cut down (debased) to very small amounts in coins and replaced with copper. http://www.gold-traders.co.uk/gold-information/medieval-money-and-coins.html

In the Chroncles of the Princes (Ystrad Fflur) is states for 1279

“In this year king Edward had his money changed, and the halfpenny and the farthing were made round. And then was verified the soothsaying of Myrddin when he said, ‘The form of exchange shall be split, and its half shall be round.'”

Throughout the Middle Ages, money was rarely used in Wales in any quantity, even through the time of Llywelyn ap Gruffydd. Instead, cattle was one of the primary sources of exchange: “Glyn Davies in his History of Money quotes linguistic evidence to show just how ancient and widespread the association between cattle and money was. The English words “capital”, “chattels” and “cattle” have a common root. Similarly “pecuniary” comes from the Latin word for cattle “pecus” while in Welsh (the author’s mother tongue) the word “da” used as an adjective means “good” but used as a noun means both “cattle” and “goods”.”

“… the evidence amounts to one virtually certain coin, one very doubtful coin of a doubtful prince, one well-attested lost piece of Llywelyn the Great and some lost triangular curiosities. With Norman and Angevin mintings in Wales, the evidence, though still uncomfortably scanty, is much more circumstantial.” (page 201). English coins may have circulated in Wales to some extent before the conquest, but even as late as the 14th century payment in cattle was still very common.” (See Davies, R.R. The age of conquest: Wales 1063-1415. Oxford: O.U.P.,1987).

http://projects.exeter.ac.uk/RDavies/arian/welsh.html

Archaeologists are generally working on the assumption that native rulers did not mint their own coins, having knowledge of only one instance (Llywelyn the Great).  “The changing nature of commerce in early medieval Wales has been highlighted by a re-assessment of Viking-age hack-silver and coins in the light of recent finds (Redknap 2009b). This has shown how the Viking-age silver economy in coastal Wales mirrors the progression in Ireland and elsewhere – a transformation from a late ninth/early tenth-century bullion economy to a more sophisticated one in which coin began to be retained. Besly (2006) has also summarized all single Anglo-Saxon coins from Wales, as part of a wider survey down to the thirteenth century.”  http://www.archaeoleg.org.uk/pdf/reviewdocs/earlymedreview.pdf