COINS with rare designs are known to fetch thousands of pounds at auction but ones that have been minted with a mistake on them are also selling for a lot of money.
The Royal Mint manufactures 3million to 4million coins a day, so you can see why sometimes things go wrong during the minting process.
But it's pretty rare if a batch of error coins makes it into circulation, which makes them very attractive to collectors.
To help you know which coins to look out for we've teamed up with money expert Colin Bellamy from Coin Hunter to put together a list of the most valuable "error coins" and a guide price of what they're worth.
It may be time to check your change because you could be sitting on a fortune - here are the top 10 in order of their expected value.
1. London 2012 Olympics Aquatics 50p first design worth up to £1,500
To celebrate the 2012 London Olympics, The Royal Mint released a 50p piece with 29 different designs.
But experts have valued this one to be worth between £1,000 and £1,500.
Originally, the aquatics coin shows water passing directly over the swimmer’s face, but it was modified to include less water so you can see the swimmer more clearly.
Coin Hunter said: "Beware! There are large numbers of copies of this coin, some sellers list items to deceive people into thinking they are buying a real Royal Mint produced coin.
"Stay away from eBay listings. Your best bet may be a car boot sale."
2. 1983 New Pence 2p coin worth up to £1,250
A rare batch of 2p coins can fetch some pretty serious cash on eBay - one has just sold for £100, but Coin Hunter reckons a circulated version is worth more - between £1,000 and £1,250 in fact.
The secret lies in the date. All 2p coins minted between February 1971 and 1982 should say 'new pence' on the front, while those released after this date say 'two pence'.
But in 1983, a glitch meant a batch of 2p coins were printed with the old wording - new pence - on them, rather than two pence, making them valuable to collectors.
Coin Hunter said: "To have the best chance of finding this coin, keep an eye on new eBay "buy it now" listings.
"Use search terms such as '1983 Martini' or '1983 Heinz' and sort by newly listed. These brands released sets for coin collectors and they may include the error coin.
"By entering these search terms in eBay - or having eBay notify you of new listing containing these words - you can be the first to spot a buy it now listing for a set that contains this error coin.
"These standard 1983 sets sell for £10 so you could find a bargain if you can find one containing the error coin for that price.
"They have been listed in the past at low prices by people who have not heard of the 1983 New Pence 2p."
3. Silver 2p (1971 to 1992) worth up to £1,000
These coins could be worth a fortune because they were accidentally printed onto the wrong base - copper instead of silver.
The coins have a different "tails" design to the other silver 2p error coin detailed below, as they were minted up to two decades before between 1971 and 1992.
James Weller from Kent found one in his change at home, and it could be worth up to £1,000.
Coin Hunter said: This coin could be worth anything between £200 and £1,000.
4. All zinc £2 coin worth up to £800
The rare Standing on the Shoulders of Giants £2 coin has only been stamped on nickel brass, rather than on two types of metal - nickel brass and copper zinc.
The best way to find out if your 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.
Approximately 10,270,000 of this type of coin was issued for circulation in 2007 but the experts over at GoCompare's Coining It In and coin traders at Chards hadn't even seen it before we showed them one our reader had found.
Coin Hunter said: "In 2016, Chards estimated this coin to be worth in excess of £1,300 - but as this coin has not seen much press attention, an example coming to market now may sell for between £200 and £800."
5. Bronze 20p worth up to £750
One of the rarest coins ever, the bronze 20p coin is dated 1987.
After collector David Crosier found the coin, the Royal Mint confirmed it was a mistake.
It said it was the result of an extremely rare minting error, with a blank 1p somehow finding its way into the presses and ending up with a 20p struck onto it.
A similar 2p coin sold for £1,350 so this one could be worth as much.
Coin Hunter said: "Always look for coins that are not even near to the colour they should be, looking for a not quite round 1p may help you find this one."
6. Silver 2p (1992 to 2018) worth up to £600
This rare misprint happened at the Royal Mint back in 2016 and you could easily mistake it for a 10p coin.
It has the same design as a normal 2p piece minted between 1992 and 2018 but has been accidentally minted onto a silver base, rather than a bronze one.
One sold on eBay for £1,350 after a pensioner found it gifted in a charity collection tin.
Coin Hunter said: "To have the best chance of finding this coin, remember this looks like a 10p, so check all recent (since 1992) 10p coins that have one lion on, as the wording TWO PENCE would be harder to spot at a glance."
7. £1 coin with two dates worth up to £500
These rare £1 coins have the latest design (from March 28, 2017) and are printed with the year 2016 printed on the face.
But if you look carefully - you'll probably need a magnifying glass - 2017 is printed in micro-lettering on the reverse side.
A veteran coin expert has labelled the rare find as one which could fetch up to a cool £3,000 - but only if it's verified by the Royal Mint.
Coin Hunter said: "The coin is worth anything between £250 to £500."
8. £2 coin with the Queen's head upside down worth up to £90
A small number of 2015 Britannia £2 coins showing the Queen's head upside down are in circulation, and they could be worth a small fortune.
Just one in around 200 of the coins shows the Queen’s head rotated clockwise by around 150 degrees, making it very rare.
The Royal Mint has said the misalignment was "almost certainly the result of one of the dies working loose and rotating during the striking process".
While we don't know how much these coins could fetch on eBay, similarly rare £2 coins with errors on them - such as one released in 2007 to mark the 200th anniversary of the 1807 Abolition Of The Slave Trade - have been offered on the auction site for £300.
Coin Hunter said: "Full 150 degree rotation coins are worth around £60 to £90. Coins with less rotation are worth in the region of £20 to £30."
9. Undated 20p coin worth up to £60
Back in 2009, the Royal Mint accidentally issued up to 200,000 20p coins issued without the year stamp – making them worth at least £50 each.
It’s well worth rummaging through your silvers to look for the rather rare coin, as the 2009 undated 20p became the first coin in over 300 years to enter circulation without a date stamped on it.
The dangers of selling your coins on eBay
THE most valuable coins are usually those that have low mintage numbers or those with an error.
These are often deemed the most valuable by collectors.
Once you’ve found out whether the coin is real or not, you have a number of options - either selling it through a coin dealer, at auction or on eBay.
Sell it at auction
If you’ve got a coin that you would like to sell at auction then you can contact a member of the British Numismatic Trade Association.
They usually deal in very old coins but they may be able to help you assess whether it’s worth selling your coin at auction or whether it would be valuable to a collector.
Sell it on eBay
If you want to sell the coin you’ve found in your spare change on eBay then you need to know the risks.
Remember to set a minimum price that is higher or at the very least equal to the face value of the coin.
Even if your coin “sells” on eBay for a high price there’s no guarantee that the buyer will cough up.
In its terms and conditions, the auction website states that bidders enter a “legally binding contract to purchase an item”, but there’s no way to enforce this rule in reality.
The most eBay can do is add a note to the buyer's account about the unpaid item or remove their ability to bid and buy.
This is because in order to sign up to the website, users do not need to put in valid bank or PayPal details before making a bid.
If a bidder refuses to pay, then the only option for sellers is to give “second chance offers” to other bidders or relist the item.
For items of a high value, eBay recommends that sellers put a limit on their listing to approve bidders.
It means bidders must email you before placing a bid but NOT that they must pay out the cash if they win.
Mint condition undated 20ps could even fetch as much as £100 - but the pros think it's worth between £40 and £60.
Coin Hunter said: "To check 20p coins quickly, do not look for a date as the date can be top left or bottom right.
"Find the new designs and flip the coin over to check if ELIZABETH is written across the top. This will be an undated 20p."
10. First World War Centenary Royal Navy £2 coin worth up to £10
This £2 coin is the second in a five-coin series remembering the First World War. There were only 650,000 of them minted, making them the third rarest £2 coin.
While they fetch around £3 on eBay, it's the ones with a "flag error" that are the most valuable, which could be worth up to £10.
Coin Hunter said: "Here at Coin Hunter we have seen at least 50 of this coin design, but the "flag" error was present on just one coin, with two others having a small deposit of metal in the same area."
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