A TINY unremarkable error on your 20p coin makes it worth 485 times its face value as a fiery eBay bidding war reveals

One mistake made for the first time in 300 years caused 250,000 "mule" coins to become a collectors item - cue to check pockets now.

A minuscule error on your 20p coin could make it worth 485 times its face value, as a fiery eBay bidding war has revealed.

The mistake, made for the first time in 300 years, saw 250,000 "mule" coins become a collector's item - so get checking those pockets now.

After a fierce bidding war on eBay, one savvy seller flogged their rare 20p for a grand total of £97.

At first glance the coin may seem totally normal, but take a closer look and you'll notice a key piece of information is missing.

Prior to November 2008, the Royal Mint switched the position of the date on the 20p coin from tail to head.

However, this batch of coins failed to get the memo.

They were minted without a date on them at all.

And now, one has sold on eBay for 485 times its worth.

It comes after another savvy seller flogged a rare coin for 300 times its worth.

The unusual 50p sold for a grand total of £135 on January 16 - and it features an architectural masterpiece which lies in London's famous Kew Gardens.

The 50p coin, which could earn you hundreds of pounds, features Kew Gardens' iconic Chinese Pagoda.

The Chinese Pagoda, a Grade 1 listed building was constructed in 1761 as a gift for Princess Augusta of Wales.

It also features a "decorative leafy climber twining in and around the tower".

Along with the markings 1759 - to represent when the gardens were founded - and 2009 - for when the coin entered circulation.

One savvy seller took to eBay to flog their 2009 coin.

It sparked an eBay bidding war, with 13 eager collectors desperate to snap it up.

The lucky new owner was sent it in a display box.

When it comes to bidding on eBay, the seller usually sets a starting price and buyers place bids to compete with each other.

The highest bidder wins the auction and bags the item.

How to check the value of your spare change

Coins with rare designs or to commemorate historic figures and events such as The Olympics often attract high values.

You can use experts like Coin Hunter to check over your change and see how much it could be worth or refer to the Changechecker scarcity index.

It is also worth looking at how other rare coins have sold on eBay

Watch out for fakes though.

Get your coin verified by The Royal Mint to reassure buyers that they're paying for the real deal if you try to sell it as this can bump up the price.

If bidding on a coin, check how many others are interested as this can provide an indication of how valuable and genuine a coin is.

This is a good idea to help push up the price too as you can advertise it as genuine.