The new 20p mule, like all truly accidental mules, is very interesting. I write to correct Chris Hill who was quoted as saying that the previous UK mule was a 2 p piece of the 1980's. There was a more recent mule: the 1994 Bank of England proof gold two pound piece.

The normal base metal currency piece had its own obverse. For about half of the thousand or so gold proofs struck, an obverse die was mistakenly employed that was meant for a gold double sovereign with a St. George and the Dragon reverse. The standard catalog published by Spink includes this mule.

At the time of issue, the Mint sent a letter to purchasers of the gold proof version of the Bank of England two pound piece apologizing for the mistake and offering to replace the mule (not called that in the letter) with a piece with the intended obverse. I have not been able to learn how many purchasers of the mule accepted the Mint's offer to replace it.

As it is undated, how do we know the missing date is 2009? The error came to light some time ago (only the publicity is recent) and they are more likely to be missing the date 2008 - the year when both old and new styles of coin were made.

I couldn't remember when I first heard about it, but this Daily Telegraph article contains a Royal Mint statement that the error occurred in 2008 If the fellow in the pub was offered £500 he should have taken it, when the hysteria dies down I reckon they will be worth about $20.

It was to be expected. Once the word of the "dateless 20p" got out everyone in the U.K. is looking at their coins. Here is a story of a Bridgewater woman who found an error coin in her cash register some time ago, but is now looking for a buyer.