It's illegal to make or use counterfeited coins and the Royal Mint says people must hand them in if they think they have one. But how can you tell?
It all depends on the quality of the counterfeit, but key signs include a poorly defined ribbed edge, the wrong typeface and an indistinct design or bust of the Queen. A fake can also be slightly different in colour.
"Current fakes are what we call 'soapy' in the coin business," says Garry Day, who works for a leading coin dealer, AH Baldwin.
"This means the marking and detail on them, like the queen's head, are blurred and not very distinct."
Another way to identify a fake is to check the alignment of the coin. Hold it so the Queen's head is upright and facing you - when you turn the coin over, the pattern on the reverse should also be upright. Fakes can often be at an angle.
The Royal Mint's online design portfolio can also be used to easily identify what's genuine and what's not. Since they were introduced in 1983, the design on the reverse of the coins has changed every year.
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Often the year and the design do not correspond on a fake. Also, the Latin motto on the edge of the coin should correspond to the right year.
A simple test at any automated vending machine can also identify a suspect coin. A lot of counterfeit coins are rejected, often leaving you grappling to find another coin in your purse or pocket.
But ultimately, how easy it is to identify a fake comes down to its quality. The good news is the fakes are getting worse, according to some experts.
"Quality is definitely dropping and fakes are now quite obvious, even to the untrained eye," says Mr Day, who has been studying the problem.
"The workmanship isn't what it used to be and most are pretty easy to spot. People just need to know what they are looking for."
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