Buried in a hurry – but it took a millennium to find

Unique collection discovered by metal detectors casts new light on the Vikings

The "largest and most important" Viking hoard found in Britain since 1840, which could shed new light on the historical period, will go on display in London and in York after careful conservation work.

The treasure, probably buried in a hurry by a wealthy Viking in Northumbria after the Anglo-Saxons had invaded the region, could reveal lost historical secrets, according to an expert at the British Museum. The museum has acquired the £1m hoard jointly with the York Museum Trust in Yorkshire.

The "once in a lifetime" find, which could redraw historical lines of Anglo-Saxon conquest over the Vikings in 10th century Britain, has been valued at £1,082,000. It was discovered in a field in Harrogate, North Yorkshire, by a father and son metal-detector team in January 2007, who will now share the money with the owner of the land on which the precious antiquities were found.

The hoard – which includes a silver cup estimated to be worth more than £200,000, as well as 617 coins and various silver fragments, ingots and rings, will go on display in both York and in the capital after careful conservation work which began a month ago.

Experts hope the process will reveal crucial details about the Viking era. Initial examinations suggest the treasure dates to 927 or 928. Conservation experts have already revealed remarkable insights: the cup, which has been gilded inside and out, is most likely to have belonged in a church, with vines decorating its exterior – a Viking symbol of Christ. Some of the coins shed new light on the period – parts of Britain such as Staffordshire and Yorkshire were already believed lost by the Vikings and under Anglo-Saxon dominion, yet there are coins which show the Vikings were still creating their own currency in these regions. One such coin, with the word "Rorivacastr" on it, is believed to have originated from Roceter, in 10th-century Staffordshire, on the border of Viking and Anglo Saxon control.

Gareth Williams, curator of early medieval coins and Viking expert at the British Museum, said this particular coin revealed that the region may still have been under Viking control, despite Anglo Saxon spin that it was under their rule. He added that it was a truly remarkable find, with a vast array of coins from as far afield as Scandinavia, continental Europe, Tashkent and Afghanistan.

"There's been nothing like it for over 150 years. The size and range of material gives us an insight into the political history, the cultural diversity of the Viking world and the range of cultural and economic contact at that time," he said. Priceless lessons in history would further be revealed in four years time after careful study, he added.

Most items were preserved because they were in the cup. "The cleaning process has shown it was an even more remarkable find than we first thought," he added.

David Whelan, and his son, Andrew, from Leeds, who discovered the buried bundle, said it had initially felt like an unlucky day when they drove out to the countryside with their metal detectors one Saturday morning in January. They had been turned away from two farms and had had a squabble before reluctantly visiting a field as a "last resort" because they had only ever discovered buttons there.

The pair then unearthed treasure so rare it is only the second of its kind found in Britain, and is among six or seven in Europe. Andrew Whelan said: "Being keen metal detectorists, we dreamt of finding a hoard but to find one from such a fantastic period of history is just unbelievable. The contents went far beyond our wildest dreams and hopefully people will love seeing the objects on display in York and London for many years."

The treasure is believed to have belonged to a rich Viking who buried it during the unrest following the conquest of the Viking kingdom of Northumbria in 927 by the Anglo-Saxon king Athelstan.

Mary Kershaw, director of collections at York Museum, said: "The Vale of York Viking hoard will greatly add to the understanding of the early 900s in Yorkshire and its connections with the world."

The treasure will go on display at the Yorkshire Museum in York from 17 September until November, when it will be moved to the British Museum.