People are being urged to check their pockets, piggy-banks and down the back of the couch after a rare 50 pence piece has sold for 240 times its value.
A rare 50p coin featuring Sir Isaac Newton recently sold on eBay for £120 and people could also have one worth £245 in their spare change without even knowing it.
So it is worth checking the design of any 50p coins to see if one of them could be among the rarest and most valuable ones in circulation.
While the most sought-after 50p - the Kew Gardens design - can fetch up to £245 on the likes of eBay, other rare 50p coins usually achieve a premium of around 10 to 12 times face value, or £5-£6, when they are sold on.
It goes without saying, perhaps, but the rarer the coin the more it is worth and experts at Changechecker.org have created a scarcity index that tracks which circulating 50p coins are the most scarce and collectable.
The index uses a unique combination of mintage, collecting and swap data to give the most up-to-date picture of today’s 50p coin collecting market.
The aforementioned Kew Gardens 50p tops the scarcity list. With a mintage - which means the number of coins issued - of just 210,000 it is the rarest coin and, therefore, the most in-demand.
The next nine scarcest coins are all from the 2012 Olympics.
Football, Triathlon, Judo, Wrestling 50 pences will sell for between £8 and £21 on eBay or up to £33 for a set of four.
If anyone discovers they have a rare 50p, they can either choose to sell the coin on eBay or through a specialist like ChangeChecker.org.