Why did royal British coin fetch a record £430,000?

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The coin

A British coin sold at auction for a record-breaking £430,000, at Baldwin's auctioneers in London. After fees, the buyer will pay £516,000. This makes it the most expensive modern coin minted in the UK ever to be sold.

So what's so special about it, and how does it compare to the most expensive coins of all time?

The coin

The coin is incredibly rare - in fact it is only one of two in existence. According to Coin Update news, it was a 'proof' for a gold sovereign which was meant to be produced to commemorate the coronation of Edward VIII in 1937.

However, Edward abdicated in 1936 to marry his American divorced fiancee Wallace Simpson, so the coronation never happened and the coins were never made. The 'proof' was last sold in 1984, when it fetched £40,000.

The new figure stands in stark contract to the £1 million banknote up for sale last month with a valuation of just £10,000. The difference is partly to do with the fact there are simply more coin collectors than bank note collectors - there are millions of people trying to add something special to their collection.

Most expensive

However, it is far from the most expensive coin sold at auction. According to the Guinness Book of Records, the most valuable coin ever sold was the 1933 Double Eagle, a $20-gold coin which was sold in New York in 2002 for $7.59 million.

In 1933 President Franklin D. Roosevelt took the US off the gold standard and ordered that all 1933 golden double eagles be destroyed - except two to be preserved in a museum. Somehow ten survived, nine were destroyed later when they resurfaced, but one was exported to Egypt before the mistake was discovered.

After the King of Egypt was deposed in 1954, the coin disappeared again, until a man was arrested for trying to sell it in New York. From there it was moved to the Treasury Department in the World Trade Centre, where it was only removed eight months before the buildings were attacked. The coin was made legal tender after the 2002 auction.

The most expensive British coin ever sold, meanwhile, was an Edward III medieval gold double florin known as a double leopard because of the crowned leopard heads on each side. It was made around 1343 and sold at auction for £460,000 in 2006 - three times the estimate placed on the coin. It had been found by a metal detecting enthusiast in the south of England - but the location was never disclosed in order to prevent a flood of metal detectors descending on the area.

The most expensive coin to feature a British monarch was actually minted relatively recently in 2007 - in Canada. It was the world's largest gold coin, with a Canadian $1 million face value, which sold at auction for $4 million in 2012. There were five of the coins made, one of which is owned by the Queen. This one was owned by an investment company which went bust.