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The little coin, pictured right, which weighs just 4.33gm and measures only 3/4in (20mm) in diameter, was discovered in 2001 in Bedfordshire by an amateur metal detectorist near a public footpath beside the River Ivel and is being offered for sale at Spink by agreement with the landowner.

As silver was the chief coinage of Europe at this time, gold survivors are rare, but this particular penny is in a remarkable state of preservation and has a number of especially desirable features. This has prompted the auctioneers to predict a price in the region of £120,000-150,000.

The obverse bears a very fine titled bust portrait of Coenwulf, King of Mercia (who reigned from AD796-821), while the reverse features a central floral design surrounded by the legend DE VICO LVDONIAE (from the wic of London). Although Coenwulf silver coins are known, this is his only known gold coin and the first to bear a proper portrait of an Anglo-Saxon ruler. The London legend to the reverse is just as exciting. This is the only known gold coin bearing a London mint signature between the gold shillings of c.AD 630 and Henry's III's gold penny of 1257. It is also the only coin to refer to London's wic (the Anglo-Saxon trading settlement outside the old city walls and west of the old Roman city).

Only seven other Anglo-Saxon gold pennies are known to exist. As six of these are are in the British Museum and the seventh is in the Cantonal Museum Lausanne, Spink's example represents the only opportunity for a collector to acquire one.

The coin will feature in the Spink auction on October 6 and 7, which is timed to coincide with the Coinex Fair.