A metal detectorist discovered a giant gold coin - the first of its kind to be found in Britain - the day after his 35th wedding anniversary.

The £30,000 treasure is believed to have originated in 15th Century Portugal and is inscripted with the phrase 'In this sign shall we conquer' in Latin.

Civil Servant Mick Edwards’ find weighed in at over 30 grams, double the largest gold coin circulating in England at the time - meaning it was once worth over two pounds.

The site was land which belonged to the Ernle family from 1489 until 1928, in Etchilhampton, near Devizes.

The Wiltshire Gazette and Herald: SWNSSWNS (Image: SWNS)

Experts from London auctioneer Noonans said its 10 Cruzados piece from the era of Manuel I, who reigned from 1495 to 1521, and a test-punch has clearly dented the top right.

Over the Latin inscription on the 36 millimetre coin lies a cross of the Portuguese Order of Christ Cross and the flipside features the crowned royal arms of the same country.

Mr Edwards, 62, from Durham, had been metal-detecting for a decade to help recover from an painful illness affecting his kidneys, caused by diabetes.

Because of the pain he can't sit down for long and metal detecting keeps him mobile.

The Wiltshire Gazette and Herald: SWNSSWNS (Image: SWNS)

Just before the find he had bought a Deus II detector, and went out searching with it during a trip to Wiltshire to celebrate 35 years of marriage.

After little luck Mick went to the top of the field for one last push before breakfast, when he heard the beeps. He dug 10 inches in the dirt and saw the coin.

The team at Noonans told him it was struck in Lisbon using gold recovered by Vasco de Gama during his voyages to Africa and India.

De Gama was a 15th Century explorer, and in 1497 became the first person to sail from Europe to India.

Mick said: “I was staying on the farm near Etchilhampton in Wiltshire with my wife after celebrating 35 years of marriage from the day before.

The Wiltshire Gazette and Herald: SWNSSWNS (Image: SWNS)

“So far I had only found some broken crotal bells, so I walked to the top of the field for a final effort before breakfast, taking just three more steps I received a clear signal which sounded like a large copper coin.”

“I was dumbstruck and just sat looking at the coin unable even to breathe. I could see the cross on the coin and thought it was probably Spanish but later found out it was Portuguese from the King’s name Manuel.”

Noonans estimate the value as between £20,000 and £30,000, and are putting it up for auction on Thursday September 29 in their two-day sale of coins and historical medals.

Mick’s wife is compiling the list of how she would like to spend the cash and one half of the proceeds will go to the landowner.

Nigel Mills, artefacts and antiquities consultant at Noonans said: “The coin features the crowned royal arms of Portugal on the obverse with the cross of the order of Christ on the reverse with the Latin legend translated ‘In this sign shall we conquer,’ with a test punch on the reverse."

He added: “In England at this time the largest gold coin was a Sovereign which weighed 15.3 grams so this coin is more than double that in weight, so would have had a value greater than two pounds.”