Elizabeth II (1952-), Twenty Pence, c. 2008, an undated mule (S.4631A), extremely fine, the first currency coin struck without a date for circulation in Britain since the reign of Charles II.
Following the redesign of the standard circulating coinage for Britain in 2008, the date was moved from the reverse of the Twenty Pence design to the obverse. Inadventently the old obverse was muled with the new reverse design by Matthew Dent to create the first British coin struck for circulation that bore no date in over 300 years. It is not known how many were released into circulation.
Estimate: £30 - £40