RARE coins can sell for thousands of times their face value - and it's always worth seeing if you've got any lying about.
One coveted 2p coin garnered the interest of collectors across the world due to its unusual wording and sold for £700 at auction.
Going under the hammer at RWB Auctions on September 25, the copper sold for a whopping 35,000 times its original market value.
It is easily identified by three words as an error from the UK's Royal Mint means that the 2p coin reads "new pence" instead of "two pence".
Collectors say this subtle error was likely produced when an old die was used to strike the coin, and very few of these coins exist.
The handful of these coins can be found in sets produced in collaboration between The Royal Mint and Italian drinks company Martini & Rossi.
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They were made as part of a promotional giveaway labelled 'The Great British 1983 Coin Collection' on the cover.
But although thousands of the sets were released, only a small number feature the rare 2p coin.
“It is worth checking old coin collections for this set, particularly if you were born in 1983," said Jon White, of RWB Auctions.
"Someone may have bought you one as a baby or as a Christening present. If they happened to get hold of a rare one, then you have a very valuable gift on your hands.”
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The auction house has previously sold a scarce Lord Kitchener £2 for £1,000 and an unusual Olympics 50p for £1,500.
How to spot rare coins and banknotes
Rare coins and notes are highly desirable among specialist collectors and could make you a mint if you find one.
Some of the most in-demand pieces can sell for hundreds of pounds.
If you spot an unusual-looking coin in your change, keep hold of it.
Then look up exactly how rare it is. Usually, the rarer it is, the more valuable it is.
You can find out what coins are rare and how they look on The Royal Mint's website.
You can also determine the coin and how common it is by looking at the scarcity index on specialist coin collector sites.
How can I check if my error coin is genuine?
RARE and valuable coins can go for a hefty sum - but how do you know if your coin is the result of a genuine minting error?
The best way to find out if you have an error coin is to send it to the Royal Mint museum, which will analyse it and see if it is a result of a genuine minting error or not.
It'll normally take a couple of weeks to get the results back to you.
But remember, there's a difference between a genuine error coin and one that is just imperfect, for example with a design that is not as clear as you'd expect.
And whatever you do, don't be tempted to splash your cash without evidence from the Mint confirming that it's a genuine error.
To work out how valuable it might be, take a look at similar coins that have recently sold on eBay or even at auction.
Remember to look at "sold listings" to be sure that the coin has sold for the specified amount rather than just been listed.
It's not just coins, rare notes can sell for multiple times their face value.
This includes fivers, rare £10 notes as well as higher denominations.
One of the main distinguishing marks of a rare note is the serial number.
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These numbers can be found on the side with the Monarch's face, just under the value of £10 in the corner of the note.
Low serial numbers or something quite quirky can see you cash in thousands.