Shoppers told to keep an eye on their loose change in case this elusive 50p that sells for 250 times its face value crops up

This rare coin has been soaring in price on eBay and might be down the back of your sofa

Keep an eye on your loose change incase this elusive 50p that sells for 250 times its face value crops up.

This rare coin has been soaring in price on eBay and might be down the back of your sofa.

In 2009 the Kew Gardens coin was released to mark the 250th anniversary of the historic botanical garden in southwest London which opened in 1759.

Highly prized by collectors, the celebrated Kew Gardens coin has skyrocketed in great demand since its release.

The Royal Mint released around 210,000 copies of the coin which makes it one of the rarest coin available.

One side of the coin shows a the portrait of Queen Elizabeth II, while the reverse showcases the Chinese Pagoda at the Royal Botanic Gardens, surrounded by two intertwining stems.

If you happen to stumble across a Kew Gardens 50p in your pocket, or tucked away in your glovebox, it could fetch far more than its face value.

At 250 times its original value, it’s definitely one to save rather than spend.

Most recently on eBay, one lucky seller attracted 20 bids on the coin before selling it for £139.

In the past these coins have sold for up to £700 on eBay.

It was once considered the rarest coin in the UK, with only a limited number in circulation following its production.

Today, the title of rarest coin is believed to belong to a 50p featuring the Atlantic Salmon and bearing the King's portrait.

What makes a coin rare?

One of the most common types of coins to collect are 50p pieces.

This is due to their large surface area, as there is enough space to add designs to.

With a 27.5mm diameter, it's the biggest British coin and is used to celebrate big events like anniversaries, historical occasions, or sport fixtures.

During the Olympics, a range of themed 50p coins were printed - with the Aquatics 50p reaching up to an eye-watering £2,000 in auction.

This coin jumped in price due to an initial design error, which was quickly corrected, leading to very few misprints in circulation.

Mistakes make a coin unique as they will most likely be worth more, as there a fewer of them.

Even without a design error, if a coin has a low mintage there are fewer of them in circulation and so are deemed rare.

By and large, the rarer the coin the more valuable they are to collectors.

How to spot valuable items

COMMENTS by Consumer Editor, Alice Grahns:

It’s easy to check if items in your attic are valuable.

As a first step, go on eBay to check what other similar pieces, if not the same, have sold for recently.

Simply search for your item, filter by “sold listings” and toggle by the highest value.

This will give you an idea of how much others are willing to pay for it.

The method can be used for everything ranging from rare coins and notes to stamps, old toys, books and vinyl records - just to mention a few examples. 

For coins, online tools from change experts like Coin Hunter are also helpful to see how much it could be worth.

Plus, you can refer to Change Checker’s latest scarcity index update to see which coins are topping the charts. 

For especially valuable items, you may want to enlist the help of experts or auction houses. 

Do your research first though and be aware of any fees for evaluating your stuff.

As a rule of thumb, rarity and condition are key factors in determining the value of any item.

You’re never guaranteed to make a mint, however.

How to sell a rare coin

Handy auction websites like eBay, Facebook marketplace, or trading apps can be easy to use - but there are risks.

Even though these sites are somewhat regulated, fraudsters may try and target sellers by asking to purchase the item and ask for money upfront for a courier.

You might find yourself waiting for them to show up as they're only claiming to use a courier to nab some cash.

Links, payment URLs and transaction portals sent online are also risky and it's advisable to meet up face to face.

Expert sellers sometimes recommend handling cash to limit the risk of online scams.

It's often advised to take your rare coins to an auction to be safe.

Getting a specialist opinion through The Royal Mint's Collectors Service can help you authenticate and value your coin.

Hitting the rare-coin jackpot could see you cashing in thousands if you get your hands on the right one.