An “extra-special” rare 50p coin inspired a mini-bidding war on eBay before selling for £4,000 last week, as Brits are being encouraged to check their change.

You might have a small fortune lying around in your house after a commemorative 2012 Olympic 50p coin sold for 8,000 times its face value in September.

The coin marked the London games with an image of a swimmer on the tail side.

The coin was designed in 2011, and previously described by the Royal Mint as “extra special”.

Sudbury Mercury: The “extra-special” 2011 Olympic Games aquatics 50p coinThe “extra-special” 2011 Olympic Games aquatics 50p coin (Image: Royal Mint)

They explained: “The design was created by Jonathan Olliffe, and it depicts a swimmer in action with fluid lines struck into the metal representing the waves.

“In the rare first design, these lines covered the swimmer’s face. Soon after its release, the coin was tweaked to make the face more visible, but not before the first design made it out into the world.

“One of the most exciting aspects of this special 50p is that no one knows exactly how many entered circulation before the changes were made, only that numbers are extremely limited.

“This is often the case with error coins, and they immediately become a collectable piece. Few have ever been sold and many take pride of place in private collections, but there’s always a chance this valuable coin could find its way to you.”

Attracting attention from keen collectors, the coin, with lines covering the swimmers face, inspired a mini bidding war with 28 bids placed during the online auction before selling for £4,000.

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.

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:

  1. Olympic Aquatics (2011), unknown
  2. Kew Gardens (2009), 210,000
  3. Olympic Wrestling (2011), 1,129,500
  4. Olympic Football (2011), 1,161,500
  5. Olympic Judo (2011), 1,161,500
  6. Olympic Triathlon (2011), 1,163,500
  7. Peter Rabbit (2018), 1,400,000
  8. Flopsy Bunny (2018), 1,400,000
  9. Olympic Tennis (2011), 1,454,000
  10. Olympic Goalball (2011), 1,615,500