Auction of rare gold coin may fetch £4m

A unique coin designed by the American sculptor Augustus Saint Gaudens is expected to become the most expensive in the world when it is auctioned with an estimate of $6m (£4.2m).

The 1933 $20 gold coin, known as a Double Eagle, has never been authorised to be sold to a private owner before. After it was struck, Franklin D Roosevelt, in one of his first acts as President, took the US off the gold standard in an effort to help the American economy out of the Great Depression.

All of the 1933 Double Eagles were ordered destroyed, but 10 specimens are known to have escaped illegally into private hands. Nine of the 10 were seized by the US Secret Service during the 1940s and 1950s, and destroyed. The remaining coin's whereabouts remained a mystery for more than 60 years, until it was seized at the Waldorf- Astoria in New York in 1996, from Stephen Fenton, a British dealer who was attempting to sell it to Secret Service agents posing as fellow dealers.

After a five-year legal wrangle, a settlement was reached between the US Justice Department and Mr Fenton for the sale. The coin, held in Fort Knox, will be sold on 30 July at Sotheby's in New York.