if you see a UK 20p piece advertised on ebay with no date on the reverse advertised, do not touch it with a barge pole. one was sold to a us buyer for £10, this coin is the standard circulating coin and is not a minting error, members of a coin forum in the UK have made a collective complaint to ebay about the seller deliberately trying to con overseas buyers by making a false declaration in his listing. if anyone really wants a 2010 20p i will send them one for free rather than this guy making a profit from unsuspecting overseas buyers.
Is the coin the ebayer was selling a 2010 coin? Or is he actually selling a real error? They DID make an error 20 pence that did not have a date on it. It was a mule struck in 2009 that has the reverse die of 2009 and an obv die of 2008. In 2008 the date was on the reverse of the coin but when they redesigned all of the coins for 2009 the date was moved to the obv. On some 20 pence pieces they erred and used a leftover obv die for 2008 which resulted in a coin with no date.