Maurice Richardson spent 40 years hunting for treasure in the fields of Nottinghamshire, unearthing little but pieces of scrap and the odd coin. Then one rainy day, using his metal detector to look for parts of a Second World War aircraft, he stumbled across the most expensive single find in recent history.

Mr Richardson, a 59-year-old tree surgeon, discovered a gold and silver torc, a necklace of eight twisted metal strands valued at £350,000 and dating from AD200 to 50BC.

The find near Newark – in a part of the country that has yielded few items of that age and value – has prompted archaeologists to rethink the importance of the entire region 2,000 years ago. It also provided Mr Richardson with a £175,000 windfall (by law the other half of the money for a treasure find goes to the landowner, in this case Trinity College, Cambridge).

The British Museum, which published the latest Treasure Annual Report yesterday, has seen a big increase in the number of finds: 749 were reported last year, compared with 665 in 2006. They credit the Treasure Act – which since it came into force in 1996 has meant that treasure hunters are compensated for their finds – and the growing number of local historians with metal detectors.

According to Barbara Follett, the Culture Minister, since the Act came into effect there has been a tenfold increase in the numbers of artefacts reported.

James Robinson, the curator of medieval collections at the British Museum, said: “The way the system works now is a massive incentive for people to go out and find things. The number of items found seems to be getting bigger and bigger every year.”

Michael Lewis, the deputy head of portable antiquities and treasure at the museum, said that treasure hunters were an invaluable local resource. “Metal detectors go to parts of the country and fields where archaeologists wouldn’t normally go,” he said. “There’s a lot of tremendous information that finders are telling us about the past.”

Mr Lewis said he suspected that a lot of treasure hunters were pursuing their hobby “to get away from their wives”, but for others it was a way of life and a way of finding and preserving the past.

For Mr Richardson, metal detecting has been a lifelong hobby and finding something of value was merely a bonus. “Week after week after week we go into the fields and find nothing. You look and look for things like this and you read about other people finding them, but it never happens to you. It’s not about the money, but the fact that it has been saved for the nation.

“I once found something that looked really interesting – gold – and when I dug it up it was the end of a curtain rail. You find a lot of little pieces but 90 per cent of it is just interesting,” he said.

The necklace, which weighs 2lb and is made of a gold and silver mix called electrum, is one of the best Iron Age torcs found in the past 50 years in Britain. Glyn Hughes, senior collections officer at Newark Sherwood museum services, who bought the necklace, said: “When we first saw it we were speechless. It was one of those once-in-a-lifetime moments. What is significant is what it tells us about the Iron Age – what it tells us about north Nottinghamshire.”

Under the Act, any gold, silver and groups of coins more than 300 years old have to be reported to the local coroner. If the treasure is bought by the British Museum or a local museum, the proceeds are split, with half going to the finder and half to the landowner.

According to the report, the East and South East are the best places to find treasure, with Norfolk, Suffolk and Kent the top spots last year. Metal detectors cost from £70. Mr Robinson’s machine was from the top of the range, and cost £1,200.

Other discoveries in the collection include a hoard of 3,600 Roman coins found at a building site in Snodland, Kent, a medieval silver seal containing the only surviving miniature portrait of the emperor who succeeded Hadrian, Antoninus Pius, and a 7th-century piece – probably part of a necklace – that was found in Essex and is worth £3,000.

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