The 20p piece is a rare “mule” coin dating from 2008, and fetched £90 at auction. The coin was minted without a date due to an error and quickly became a sought-after collector’s items.

the 20p coin sold for £90. The rarest is the Kew’s Garden 50p, which was designed to mark the 250th anniversary of the gardens in 2009. Only 210,000 coins were ever minted with this design.