The gold and silver Iron Age torc, an ancient necklace, was described as the "most valuable single treasure found in Britain in recent times" when it was unveiled at the British Museum to mark publication of the Treasure Annual Report.
The artefact, dubbed the Newark Torc, was found in 2005 by Maurice Richardson in a farmer's field in Newark, Nottinghamshire.
Mr Richardson, 59, said experts initially refused to believe the rare find was genuine.
The torc was bought by Newark and Sherwood Museums Service, with the proceeds split between Mr Richardson and Trinity College, Cambridge, which owns the land.
The Treasure Annual Report said a record 747 objects were reported in 2007. Other finds presented at the museum included a gold and garnet Anglo-Saxon mount and a hoard of more than 3,600 Roman coins.