A rare 20p coin with no date on it has sold for £44.95 on eBay.
The 2008 piece fetched more than 224 times its original face value after a collector snapped it up on September 10.
It is known as a mule coin because an accidental mix-up at the Royal Mint left it with no date on either side.
Featuring Queen Elizabeth II on the front, the coin shows part of the Royal Shield of Arms on the reverse.
A production blunder occurred in November 2008 during a redesign of circulating British coinage, when an older heads die was paired with the new shield reverse.
The Royal Mint confirmed that fewer than 250,000 coins out of 136 million 20p pieces struck in 2008 and 2009 were affected by the mistake.
A spokesperson for the Mint previously said: "In November 2008 a number of 20p coins were incorrectly minted, resulting in the coins being undated.
"This problem affected less than 250,000 coins of the 136 million 20p pieces minted in 2008-09."
Despite their appeal to collectors, the coins remain legal tender with an official face value of 20p.
The seller explained the coin was discovered in ordinary circulation with typical signs of wear, uncleaned and untampered with.
First introduced across the United Kingdom in 1982, the 20p piece has undergone several design changes over four decades.
Earlier versions displayed William Gardner's crowned Tudor double rose until 2008, when the Royal Shield design took over.
The shield reverse forms part of a composite design that combines across 1p, 2p, 5p, 10p, 20p and 50p coins to recreate the full Royal Arms.
Five Incredibly Rare and Valuable British Coins
What makes a coin valuable?
The 50 pence piece has become the most valued and collected coin in the UK, with many collectable designs appearing on its heptagonal canvas.
Its 27.5mm diameter makes it the largest of any British coin, and allows space for decorative pictures. It has often been used to celebrate big events over the past 50 years of British history.
The rarest coins tend to be of the greatest value, with the mintage (number of coins with each design made) being the fundamental attraction for collectors.
Along with the design, other aspects of the coin which increase value are the condition of the coin and whether it has an error in its design.
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The way in which it is sold can also determine the coin’s value - while some coin collectors will bid vast amounts of money on eBay or at auction, others opt for more robust valuations by selling via a coin dealer.
Royal Mint top 10 most valuable 50p coins
Here is a list of the top 10 most valuable coins, when they were made and how many were minted:
- Atlantic Salmon (2023), 200,000
- Kew Gardens (2009), 210,000
- Olympic Wrestling (2011), 1,129,500
- Olympic Football (2011), 1,161,500
- Olympic Judo (2011), 1,161,500
- Olympic Triathlon (2011), 1,163,500
- Peter Rabbit (2018), 1,400,000
- Flopsy Bunny (2018), 1,400,000
- Olympic Tennis (2011), 1,454,000
- Olympic Goalball (2011), 1,615,500