The main reason for the introduction of the new 12-sided £1 later this year is that the current one is so easy to fake.
According to the Royal Mint, there are a staggering 30 million counterfeit pound coins in circulation.
The new version has state-of-the-art security features. There's a latent image, similar to a hologram, that changes from a '£' symbol to the number '1' when the coin is seen from different angles.
Also hard to forge is the very small lettering on the lower inside rim on both sides of the coin, and the milled grooves on alternate sides. And, says the Royal Mint, there's another mysterious hidden high security feature built in.
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With the new coin set to appear next month, the old round pound will be only be legal tender until October 15 - so you'll have to spend any you've got by then.
It's illegal to spend a counterfeit £1, even if you got it in good faith. And with about one in every forty a fake, how can you tell which are real?
Similarly, the lettering or inscription on the edge of the coin may not correspond to the right date.
Sloppy manufacturing is also a sign. You should be wary, says the Mint, if the faces of the coins or the milled edge are poorly defined, or the lettering uneven or badly formed.
And look at the colour: if it's shinier than it should be for its age, there could be something wrong.
Being able to spot fakes is particularly important if you're one of the many people hoping to put together a full set of round £1 coins before they finally disappear.
In all, there are 24 different designs. Twenty belong to five different series representing the component countries of the UK; the other four are all been variations on the theme of the Royal Coat of Arms. Some are much rarer than others.
A final, twenty-fifth round pound coin was issued by the Royal Mint last year, but never entered general circulation.
The Changechecker website is encouraging people to collect the full set while they can, and has more information here.