One £2 coin is worth as much as 16 times its face value - but you'll have to look carefully to check if you've got one.
According to the ChangeChecker scarcity index, the England Commonwealth Games £2 coin is currently the UK's rarest, and can change hands for up to £32. Other rare £2 coins generally sell for between £6 and £8.
The site rates its scarcity level at 100.
"Jumping up two places and from an Index score of 81, the England Commonwealth Games £2 coin takes the crown this quarter, benefiting from extra swap interest," says Luke Hearn of ChangeChecker.
"However, there are no great surprises when you look at the other top four £2 coins, which comprise the other Commonwealth Games coins. Indeed, the average Scarcity Index Score for the four Commonwealth Games coins has jumped almost 10 points for 85.5 to 94.75."
But you'll need sharp eyes to see if your £2 coin is the England one. All the Commonwealth Games coins have the same basic design, apart from the tiny national flag to the left of the centre of each coin.
Meanwhile, Jemima Puddle-duck has been confirmed as the most sought-after Beatrix Potter 50p, thanks to the low number produced - but the Kew Gardens 50p hangs on to its top spot as the UK's most sought-after circulation coin, selling for up to £80 on eBay.
And the Sir Isaac Newton 50p makes its entry into the rarity charts at number 23, after its surprise limited release into circulation last month. "That will certainly be one to watch over next quarter," says Hearn.
The ten most sought-after £2 coins (scarcity index)
Commonwealth Games England: 100
Commonwealth Games Scotland: 94
Commonwealth Games Wales: 93
Commonwealth Games Northern Ireland: 92
First World War Centenary (Navy): 69
Olympic Handover: 67
London 2012 Handover: 60
Olympic Centenary: 58
Mary Rose: 54
Shakespeare Comedies: 50
The ten most sought-after 50p coins (scarcity index)
Kew Gardens: 100
Jemima Puddleduck: 58
Incredibly valuable coins
Incredibly valuable coins
This Australian coin was the first half crown minted under Edward VII. The price for a Melbourne coin in good condition is particularly high because around half of them were produced with faults. It’s now worth £7,500 and has risen in value some 13,789% since it was first in production
The only half crown on the list gets its position from its rarity value. However, the fact this is a silver coin rather than a gold one does affect its value - so it’s worth £10,500. It’s significantly less than others on the list - but it has still appreciated 79,445%.
This is the newest coin in the top ten, and the first year that sovereigns were produced featuring the Queen. The coin was produced in small numbers for investors - rather than for circulation - so is thought to be worth £12,500, due to its rarity.
This is another collectable gold coin prized for its rarity value. It’s worth £15,000 today and has appreciated 191,716%
This was issued in very small numbers, as it was produced during WWI. As a result, few are available - especially as uncirculated coins - so one in good condition will fetch £16,000.
This is another coin prized for its rarity, thanks to a relatively low number being minted, and more being taken out of circulation during WWI. It’s now thought to be worth £17,000 after appreciation of 42,084%.
This 1926 coin has shot up in value and is now worth £31,500. The rise in value is partly to do with a very low mintage, and partly to do with the fact that people were asked to hand their sovereigns over to be melted down during WWI, which took many of them out of circulation.
This brass threepence from 1937 has benefited enormously from the fact that Edward didn’t stick around for long to get too many coins struck in his image before he abdicated. It is now worth £45,000.
This 1933 penny has seen a stunning appreciation in value and is valued at a whopping £72,000 today. The value is due entirely to rarity. Only around seven British versions of this coin were minted, and were intended for the King to bury under the foundation stones of new buildings. They have been subject to theft, and a few are said to be in private hands now.
This isn’t the oldest coin in the list, but it was produced in a year when all gold coins were recalled and exchanged for paper money - so the vast majority were melted down. Its rarity and popularity puts it head and shoulders above the rest. It is worth an eye-watering £6,500,000, and has increased in value 2,178,885% since it was produced.