David and Andrew Whelan uncovered the hoard, which dates back to the 10th Century, in Harrogate in January. The pair kept their find intact and it was transferred to the British Museum to be examined by experts, who said the discovery was "phenomenal". It was declared as a treasure at a court hearing in Harrogate on Thursday.

North Yorkshire coroner Geoff Fell said: "Treasure cases are always interesting, but this is one of the most exciting cases that I have ever had to rule on. I'm delighted that such an important Viking hoard has been discovered in North Yorkshire. We are extremely proud of our Viking heritage in this area."

'Astonishing discovery'

Metal detectorists David and Andrew Whelan, who uncovered the treasures, said the find was a "thing of dreams". The pair, from Leeds, said the hoard was worth about £750,000 as a conservative estimate.

They told the BBC News website: "We've been metal detecting for about five years; we do it on Saturdays as a hobby. We ended up in this particular field, we got a really strong signal from the detector... Eventually we found this cup containing the coins and told the antiquity authority. We were astonished when we finally discovered what it contained."

The ancient objects come from as far afield as Afghanistan in the East and Ireland in the West, as well as Russia, Scandinavia and continental Europe. The hoard contains 617 silver coins and 65 other objects, including a gold arm-ring and a gilt silver vessel. Dr Jonathan Williams, keeper of prehistory in Europe at the British Museum, said: "[The cup] is beautifully decorated and was made in France or Germany at around AD900. It is fantastically rare - there are only a handful of others known around the world. It will be stunning when it is fully conserved."

Turbulent times

Most of the smaller objects were extremely well preserved as they had been hidden inside the vessel, which was protected by a lead container. The British Museum said the coins included several new or rare types, which provide valuable new information about the history of England in the early 10th Century, as well as Yorkshire's wider cultural contacts in the period. It was probably buried for safety by a wealthy Viking leader during the unrest following the conquest of the Viking kingdom of Northumbria in AD927. A spokeswoman for the museum said: "The size and quality of the hoard is remarkable, making it the most important find of its type in Britain for over 150 years."

The find will now be valued for the Department of Culture, Media and Sport by the Independent Treasure Valuation Committee. Dr Williams said that the British Museum and the York Museums Trust would be looking to raise the funds to purchase the collection so it could eventually go on public display.