Experts say the coin is the earliest pure gold English penny

Specialists at Spink auction house in London had expected it to fetch between �120,000 and �150,000.

American collector Allan Davisson bought the gold coin, which was found with a metal detector near the River Ivel in Bedfordshire in 2001.

It is the only known coin to bear the name of King Coenwulf of Mercia and to show a clear regal design.

Experts at Spinks had been fascinated by its reference to the "wic" of London, an Anglo-Saxon settlement outside the city walls.

The previous auction record was held by a gold coin bearing the crown of George III, which raised �170,500 in 1999.