Traditionally, the earliest forms of money thought to have been used in Britain were small rings of gold and iron bars shaped like swords.
We now know the rings date from the Middle Bronze Age, ca. 1500 - 1000 B.C. At such an early time they would have functioned as jewelry or hair ornaments. Their only possible monetary function might have been as a means of storing wealth.
Caesar mentions the iron bars in his writings, placing them as late as 55 B.C. There is no agreement about the way they could have functioned as money.