When a penny is worth £72,000

A 1933 penny - the rarest British coin of the 20th century - has just sold at auction for £72,000.

Only a handful of pennies, bearing the head of King George V, were made in 1933. Because the banks had so many pennies in stock already, there was no need to make any more.

But 'six or seven', says the Royal Mint Museum, were made for ceremonial purposes. Three were placed by the King under the foundation stones of important buildings, with two going to the British Museum and two others ending up in private hands.

Even rarer than these, though, are the four prototypes for the design - the so-called 'pattern pennies'. One is in the Royal Mint Museum, with the other three in private hands.

And it's one of these that has just sold for £72,000 through auctioneers Baldwin's - almost twice the pre-auction estimate, and £27,000 more than the last one made ten years ago.

Of the 'circulation pennies' produced for the king, one remains mysteriously unaccounted for. It was stolen from the cornerstone of the Church of St Cross in Middleton, Leeds, during building works in the late 1960s.

And, after the Second World War, there were suggestions that one or more the others might also have been unearthed during the Blitz and spent on food.

However, if you think you've got one, don't get your hopes up too much. There are plenty of Australian, British West African, Jersey or Irish pennies dating from that year.

Worse, there are many fakes: genuine pennies from (usually) 1935, which have had the year of issue carefully altered - one of these has even appeared on Antiques Roadshow.

A 1933 penny was also advertised on eBay in 2010, and caused some excitement - until it was suddenly withdrawn from sale.

Sometimes, too, one of the many facsimile copies is mistaken for the real thing and offered for sale, although experts find it easy to distinguish these.

"Take our advice, don't waste your time looking," warns bullion dealer Chard. "Looking for the Loch Ness monster is likely to be more productive, and you might catch some fish at the same time."