Ulta-rare 50p coin featuring obscured Olympic swimmer's face sells for 8,000 times its value on eBay

The 50p fetched a whopping £4,000 - due to an unusual error in its design.

An incredibly rare 50p coin has sold on eBay for a staggering 8000 times its usual value - due to an "extra special" detail.

The coin, which was released in 2011 in anticipation for the London Olympics, features a swimmer submerged in water on its tails side.

However, unlike other versions, the swimmer's face is obscured by the ripples in the water.

Shortly after the manufacturing process began, the error was corrected - meaning there are only a few hundred in circulation.

The coin attracted a fierce bidding war, with 28 enthusiasts vying for the item.

It is not the first example of its kind to sell for thousands - with another fetching an impressive £1,500 last year.

Kimberly Day, coin expert from RWB, said at the time: "Only a few hundred examples with this rare design variation are believed to have been released.

"We're delighted that this coin has raised such a sum, it's a fair price for such a rare coin and we believe it's value will only increase over time."

29 other coins were released for the Games, featuring various sports - from gymnastics to tennis to football to triathlon.

The football version coin is the rarest out of the set, according to The Royal Mint - with just 1,125,500 minted.

Outside the Olympic range, the rarest 50p is the Kew Gardens, of which there are only 200,000 out there.

The Kew Gardens piece was minted a few years earlier than the Olympic collection and has been known to sell for up to a whopping £895 on eBay in the past.

How to spot a rare coin

A coin is usually classed as rare if a limited amount were struck, or a manufacturing error occurred when they were being made.

A low mintage figure, which is set by The Royal Mint, relates to how many of a coin were made.

Generally, the lower that figure, the more buyers are willing to pay for it, although this isn't always the case.

You can find out what coins are rare and how they look on The Royal Mint's website.

The Change Checker website has scarcity indices too - these tell you how many of a particular coin were minted.

When it comes to error coins, how much you'll get for them varies from piece to piece.

What are the most rare and valuable coins?

For example, the HG Wells £2 error coin has been known to sell for up to £1,000 in the past.

Bronze 20p coins have been known to sell for up to £750 as well while error £1 coins have been known to go for up to £200 before.

How to sell a rare coin

You can sell a rare coin on eBay, Facebook, or in an auction.

If you're selling on Facebook, there are risks attached.

Sellers have previously been targeted by scammers on Facebook saying they want to buy a rare coin and asking for money up front for a courier to pick it up.

But it's a ruse to get money out of you and the courier is never sent.

To avoid this happening, it's always best to meet a Facebook seller in-person when buying or selling anything.

Ensure it's a public meeting spot that's in a well-lit area and if you can, avoid using payment links.

Most sellers prefer to deal with cash directly when meeting to ensure it's legitimate.

The safest way to sell a rare coin is more than likely at auction. You can organise this with The Royal Mint's Collectors Service.

It has a team of experts who can help you authenticate and value your coin.

You can get in touch via email and a member of the valuation team will get back to you.

You will be charged for the service though - the cost varies depending on the size of your collection.

You can also sell rare coins on eBay.

But take into account that if you manage to sell your item then eBay will charge you 10% of the money you made - this includes postage and packaging.

Always bear in mind when selling any rare coin, you will only get what someone is willing to pay for it.