A rare 1,200-year-old coin found by a metal detectorist near Warminster sold for £7,800 at an auction this morning, nearly double the £4,000 it had been expected to fetch.

The silver penny found in August was made at the West Saxon mint in Winchester by moneyer named Wihtnoth during the reign of King Egbert of Wessex between 802 and 839, more than 200 years before the Battle of Hastings in 1066.

The coin is particularly rare and valuable because there are only three other known pennies of this type made by Wihtnoth and, according to auctioneers Spink , the Warminster penny is the best preserved of the four coins.

A spokesman for Spink said that the Warminster penny is ‘in a superb state of preservation,perfectly centred and problem-free,extremely fine and excessively rare in this condition’.

Before the auction, at Spink’s saleroom in Bloomsbury, London, the coin had been expected to sell for between £3,000 and £4,000 but was snapped up by a mystery bidder for £7,800.

Spink has not revealed the name of the metal detectorist or the precise location of the coin’s discovery except that it was near Warminster.