They were produced for a Mercury Communications sales promotion, then later used for lessons in a school but slipped back into circulation in St Albans before they could be scrapped.
One giggling 10-year-old boy was reported to have given a bewildered householder a pounds 2,500 "tip".Schoolboys were said to have given wads of "cash" to beggars and taxi drivers were "tipped" in thousands.
A spokesman for Hertfordshire Police said: "As far as I am aware, there were only about pounds 200 worth in circulation."
A Mercury spokesman said: "You don't have to look very long to realise they are not real - they are play money."Reuse content