A two-pence coin cast in the wrong metal is set to sell for hundreds of pounds at auction this week.
Rather than the usual bronze, it seems that the coin was accidentally made of the silver-coloured cupro-nickel used for coins such as ten pence pieces. It's thought that a cupro-nickel blank was somehow left inside a barrel during the minting process and stamped along with all the normal copper two pence pieces.
The coin is being sold by the former manager of a petrol station in Poole. Back in 1988, he opened a new packet of two-pence pieces for the till and noticed that one was shiny and silver in appearance rather than copper. He took it out, and after some research established it was a cupro-nickel two-pence piece - something that shouldn't exist.
And the auctioneer, too was dubious.
"I have had an interest in coins for over 40 years, but this 2p takes the biscuit as I have never heard of one before the owner brought it into our salerooms for advice," says Richard Bromell of auction company Charterhouse.
"I must admit to being somewhat sceptical at first, thinking it was silver-plated, which often happens, but it is the real deal!"
As with stamps, there are various factors that influence the value of a coin. The first, and most obvious is rarity. Condition matters too - and in this case, of course, the cupro-nickel 2p is in near-perfect condition.
Surprisingly, age doesn't make much difference to the value - Roman coins, for example, can be picked up for a few pounds. But artistic or historical value will bump up the price. Earlier this year, for example, a buyer forked out over £500,000 for one of only two 'proof' gold sovereigns in existence commemorating the planned coronation of Edward VIII in 1937 - a coronation that never took place because of Edward's abdication.