At the end of last week gold was trading at $905 an ounce (£610). Selfridges insists, however, the coin is a particularly rare one that the Royal Mint no longer produces and is therefore worth £900.

Unlike traditional gold coins or bars, which are often sold as full ounces, fractional gold coins are minted in smaller sizes, such as 1/10th, 1/4th or 1/2th ounces.

If your gold bar or coins don't have a hallmark, it's likely they're fake. In the U.S., the most common hallmark for gold is "Au," which stands for Aurum, the Latin word for gold.

The coin, a gold Unite piece, has a currency worth of 20 shillings, said the British news agency SWNS, but it is expected to sell for roughly £1,500-£2,500 (about $1,800 to $3,000 in U.S. currency).

The cup, described as being no larger than a soft-drink can, contained more than 260 gold coins dating from 1610 to 1727. The stash of coins has an estimated value of £100,000 ($116,00) in today ...

In terms of value in today's money, the trove holds a spending power of about £100,000 (or $115,100). But the auctioneers expect the coins to sell for at least £250,000 (almost $290,000) next ...