In his wood-panelled office overlooking St James's Park in central London, Peter Hambro opens a cabinet of curiosities. From it he pulls a gold coin he says was minted in the area of Belgium "shortly after the year zero [AD]".

"This coin," he says, "buys the same amount of bread today as it did 2,000 years ago." Alongside it he lays promissory notes owned by his grandfather, including ones written in gothic script by defunct governments. He points to a pre-war £10 note. "That's worth about 50p now," he says. "The others are worthless."