Olympic 50p coin error could be worth thousands - do you have one in your pocket?

The 'most highly prized 50p in existence' caused a mini bidding war on eBay as it eventually sold for £4k - but do you know what to look for?

A commemorative 2012 Olympic 50p coin has sold for thousands after it was revealed to be one of the rarest 50ps in existence.

The coin, designed in 2011 and previously described by the Royal Mint as "extra special", was reportedly sold for 8,000 times its face value in September.

Marking the London games, the Royal Mint held a coin design competition as they produced 29 pieces and introduced the youngest ever designer of United Kingdom coinage at just nine years old.

This included an aquatics coin designed by Jonathan Olliffe, with an image of a swimmer in action on the tail side with fluid lines struck into the metal representing the waves.

However, in the first design lines covered the swimmers face and soon after its release it was tweaked to make the face more visible but not before it made it out onto the world.

The first design of 2012 Olympic 50p coin, which had lines covering the swimmer's face, is one of the rarest in circulation (Image: Royal Mint)

The Royal Mint said: "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."

Last month, the first design of coin caused a bidding war with 28 bids placed during the online auction before selling for £4,000.

This comes after another 2012 London Olympics coin - depicting a cartoon high-jumper drawn by a nine-year-old Florence Jackson - sold on eBay for a staggering £216.

The individual who listed the coin received 26 bids on the coin before finalising the sale on September 14.

The image was drawn by the schoolgirl for a competition organised by the long-running children's TV show Blue Peter.

The 50 pence piece is the largest of any British coin allowing space for decorative pictures meaning it has become the most valued and collected coin in the UK.