The 20p piece is a “mule” coin dating from 2008 and was minted without a date on the coin due to an error.

The mistake means the coin is considered a collector’s item.

A batch of coins was issued without dates in 2008 due to an error in the minting process.

An example of a rare undated 20p mule coin (Image: eBay/Getty/Vandervelden)

Prior to November of that year, the date on 20p coins would be found on the tail side. However, the Royal Mint switched it so that the date would now be next to the Queen’s head.

A mistake in 2008 led to the old format being used on the Queen’s side and the new........

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