A dazzling exhibition of gold and silver, 'The Wealth of the Roman World' opened last week at the British Museum. One of the 'stars' of the exhibition is a silver treasure found in this country only two years ago. Known as the Water Newton hoard, it was found near Peter-borough by an amateur archaeologist and pop singer Alan Holmes. Magnus Magnusson investigates this story of the 'Silver in the Furrow', the earliest Christian sacramental plate, now restored to its former glory.