Undated 2008 20p coin could net its owner over 250 times its face value

This was the first time something like this had happened in centuries. And as it is so unusual it has led to it being hailed as the "holy grail" of change collecting.

An unusual coin could net its owner over 250 times its face value after an error when it was made.

The rare 20p coin was one of an unknown number released by the Royal Mint without a date.

This was the first time something like this had happened in centuries. And as it is so unusual it has led to it being hailed as the "holy grail" of change collecting.

The coin was featured on Instagram by Coin Collecting Wizard who posted a video after being asked about a coin dated from 1982 - the year 20p pieces were first introduced.

They first came into circulation on June 9, 1982, 10 years after decimalisation, with the aim of reducing the weight of the money carried in purses and pockets.

But the expert said while the 1982 coin was not unusual there was one 20p coin worth much more than its face value.

He said: "So I was sent this video from earlier where this person has found a 20p coin 1982 and they are so excited. But guess what - a 20 pence coin from 1982 is just 20 pence and not rare or valuable.

"The only 20p that you need to look out for is the undated mule error worth around £50 considered by many as one of the holy grain change collecting the undated 20p is always at the top of any coin collector's wish list.

"In 2008 an unknown amount of 20p coins were struck with the wrong die resulting in no date of the obverse or reverse side of the coin. This was as a result of a mistake at the Royal Mint when the new royal shield of design was introduced.

"The Royal Mint has confirmed that this is the first time in over 300 years that a coin had enter in circulation without a date making it extremely sought after by coin collectors."

The coin collector went on to say that the coin was selling for around £50 on Ebay. However it could go for more with one buyer paying £60.51 for the sought after coin and another £59.

Others have gone even higher with one almost reaching £100. That coin sold for £97 plus £3.35 postage after nine bids.

The minting error happened when the Royal Mint changed its design for the 20p coins in 2008, moving the date from the back to the front. The old die was accidentally used in some coins which meant some were released without a date on either side.

Experts at Change Checker say the Royal Mint estimates that "no more than 250,000 coins" could have entered circulation. They said: "In 2008, the reverse of each denomination from 1p to £1 was redesigned by Matthew Dent to feature a different part of the Royal Arms Shield.

"The 20p had previously included the date on the reverse, but with the entire face of the coin now devoted to the new design, the Royal Mint produced a new die with the date on the obverse (Queen’s head) side. However, when the new Royal Shield 20p coins were struck for circulation, the old die was accidentally used, meaning a batch was issued with no date on either side of the coin."