An extremely rare medieval coin branding William the Conqueror a “b******” has been discovered and could be sold for £2,000.

The official coin was made not long after the Norman conquest of England in 1066, but it is thought some rogue versions were minted criticising the new ruler.

Experts believe a Saxon edited some of the new coins celebrating William I's reign by describing him as an "illegitimate" king.

The penny's subtle protest against William the Conqueror is up for auction could be the work of an important minter disseminating an objection to the illegitimate new king through English currency.

It also records the closest likeness of William the Conqueror at the time of the Norman conquest, second only to enhanced images of the Bayeux Tapestry, and was worth a half or full day's wages.

After the death of Edward the Confessor, Harold Godwinson was proclaimed king of Anglo-Saxon England.

Months later, Norman King William the Conqueror invaded and destroyed Harold’s army in the Battle of Hastings in October 1066.

He took the throne, but Anglo-Saxon revolts and illegitimacy claims dogged "William the Bastard's" reign.

Coins were minted immediately after William’s Westminster Abbey coronation on Christmas Day the same year.

They usually featured ‘PILLEMVS’ for William, and the phrases ‘REX ANG’ or ‘REX A’ - short for ‘REX ANGLORVM,’ or King of the English.

However, the “extremely rare” coin up for £2,000 features a mistake - or a protest.

A native Anglo-Saxon moneyer, known as Beorthmær, ditched the ‘A’ and recorded the new king’s title as ‘REX N.’

Coin experts believe this could be a subtle rebuke against William’s illegitimacy, with the ‘N’ indicating ‘REX NORMANII’, or King of Normandy.

Researchers suspect the penny could be the work of this minter successfully spreading his rejection throughout England’s south.

The ‘slip-up’ - or protest - has been found on pennies from Bedwyn, Bury St. Edmunds, Exeter, Hereford, London, Oxford, Salisbury, Shaftesbury, Taunton, Warwick, Wilton and Winchester.

It was printed at Wallingford, Oxford, the first town to back King William, potentially making the coin a pro-Saxon rebuttal from an institutionally pro-Norman town.

Wallingford was home to one of a network of mints operating across the country.

Only four Wallingford 'REX A' pennies have been found in the past 150 years.

Spink auctioneers expect the coin to reach £2,000 on March 30.

Gregory Edmund, head of numismatics at Spink, said: "Coins are wonderful and very portable windows into our shared past.

“No matter our knowledge and understanding of history, we can all appreciate their intrinsic value and this very special Penny is no exception.

“Struck in the first English town to declare for the new King after the Battle of Hastings is evocative, especially as the design is the first to be approved by the new King immediately after his Coronation on Christmas Day 1066.

“The idea of a native Anglo-Saxon seamlessly transitioning to support the new Norman regime possibly came with a subtle final protest towards the new King – not of the English - but given his inauspicious and illegitimate roots – as King of the Normans.”