A rare 2p coin from a piggy bank could rake in a small fortune, with experts predicting it's worth a staggering 20,000 times its face value. The unique coin, set to be auctioned off at RWB Auctions near Swindon today, is expected to fetch at least £400.

It was originally discovered amongst loose change in a piggy bank back in the late 1990s. The owner initially spotted that the coin was out of the ordinary, but kept it until they saw a similar coin being auctioned this year. Specialists estimate that the 1985 coin, which is silver rather than the usual bronze colour of 2ps, might command a price of around £400. Subsequent testing has verified that the coin, from 1985, was mistakenly made from cupronickel - the same material used for 5p and 10p coins. It is also suspected that there are other similar coins yet to be discovered.

Coin expert and YouTuber Christopher Collects, collaborating with RWB Auctions, said: "We know that this is not a one-off, so there are likely similar coins out there, either put aside as a curiosity like this one or still circulating.

"When coins are minted, a blank disc of metal is stamped between two dies. If the incorrect blank gets into the machine, you end up with an error coin that has a familiar design but is composed of the wrong material.

"If the wrong blank is fed into the machine, then the result is an error coin with a familiar design but made of the wrong metal.

"With modern quality control processes, most mistakes of this kind are identified quickly, but it is clear that a small number of error 2p coins were released into circulation in 1985.

"Just a few of these 1985 cupronickel 2ps have been identified over the years and they remain a scarce and exciting error, sought-after by collectors of very rare UK coins."

To verify the coin, RWB Auctions gave it to the Numismatic Guaranty Company (NGC) - renowned coin authentication service.

The NGC confirmed the metal, and the coin, now features in their worldwide registry of certified error coins.