A Norfolk, UK, man was returning home after a day out metal detecting more than 15 years ago when he discovered the disc.

“I’d had a pretty normal day, I hadn’t found much. I was walking along a footpath and I’d kept my metal detector on - I always worry I’ll miss something if I switch it off and then it suddenly started bleeping,” the 44-year-old said.

“I dug down and discovered this small metal disc covered in mud and when I brushed the mud off I saw some inscriptions, which looked a bit strange but I put it in my bag and left it. The next time I was getting ready to go out metal detecting it fell out of my bag and I decided to wash it properly and that’s when I started to become really intrigued. It was bronze and had a wonderful patina and I knew that meant it had some age to it.

“The mystery of it as good as the finding of it. It is Harry Potter material. The workmanship is incredible. I’m now in my forties and I’ve been metal detecting since I was about 8 or 9 and I have never found an object which is so intriguing.”

Dated to late 14th century the disc up for auction at auction house Bonhams which is estimating the value of the usual object, which is included in their East Anglian View sale on October 25, will sell for £3,000 - £5,000.

James Glennie, from Bonhams’ Norfolk office, said: “This is a very unusual find and it even seems to have perplexed the experts. The Norfolk gentleman who discovered it brought it into us after hearing about another rare early medieval scientific instrument which Bonhams also sold this year.”

It will be on view at the Assembly House on October 23.