Accessible gold is running out

The total volume of gold ever mined (approximately 158,000 tonnes) would form a 22-metre cube - about the size of two semidetached houses. Far more lies out of reach under the sea bed, and sea water itself probably contains a further ten billion tonnes, but the gold is so diluted that it could take months to extract enough to make a single wedding ring.

Fort Knox isn't the biggest vault

Although the famous Kentucky army base holds most of the US gold reserves (guarded by more than 30,000 troops with tanks, artillery and Apache helicopters), the Federal Reserve Bank - five stories below ground in New York - holds the world's biggest supply. Only two per cent of the Fed's 7,000-plus tonnes (700,000 bars) belongs to the US, the rest being the property of other (unnamed) countries and international organizations. There's no door - instead, a two-metre-thick steel 'plug' seals the entrance like a cork in a bottle.