A rare Medieval bishop's ring found by a retired firefighter in a Norfolk field is expected to fetch up to £18,000 at auction.

The gold ring, which has a central hexagonal cabochon sapphire with two emeralds and two garnets, was uncovered by detectorist Mark Sell, 63, in King Row, Shipdham, in 2019.

Mr Sell said he was "amazed" when he spotted some gold glistening in the mud and planned to split the money with the landowner.

The ring, which dates from the late 12th to early 13th Century, will go under the hammer at Noonans Mayfair on 26 March.

Mr Sell said he had been in the field a couple of times before, but had not found anything of importance.

After trying again for a couple of hours before it got dark one evening in November 2019, his metal detector picked up a faint signal.

He dug down about nine inches (23cm) and could not believe his luck.

"I was amazed to see a thin line of gold in the clod of mud that I had dug up, and as I wiped away the mud, I could see the bezel of a medieval gold jewelled ring," he said.

"I could also see that the ring was complete with all of the original jewels still in place and was in pristine condition."

He reported it to the landowner and it was left with the county's Finds Liaison Officer.

It was then temporarily displayed at the British Museum before being prepared for auction.

Laura Smith, jewellery expert at Noonans Mayfair, said: "The village of Shipdham was well established by the time of the Norman Conquest, extensively detailed in the Domesday Book of 1086, and at that time recorded as being within the largest 20% of settlements in England.

"This form of Medieval ring, with a principal cabochon stone - usually a sapphire - surrounded by smaller collet set satellite stones (garnets or rubies, and emeralds), can be securely dated to the late 12th or early 13th Century, and is associated with the bishopric."