A very rare large gold coin from the reign of Charles I, which was minted in Oxford, is expected to fetch £50,000 when it is sold at auction.

It is known as the Triple Unite and was issued during the English Civil War and depicts Charles I holding a sword and an olive branch – possibly signifying his desire for peace.

The coin, which weighs 26.57g, dates from 1643 and was minted in Oxford with the value of 60 shillings or three pounds.

It is being sold on September 22 at auction house Dix Noonan Webb as part of the Micheal Gietzelt Collection of British and Irish Coins.

The collection, which is expected to fetch more than £420,000, comprises 220 coins, with the main emphasis being on Charles I and others from the era of Oliver Cromwell.

Christopher Webb, from Dix Noonan Webb, said: “Far exceeding the size and value of any previous denomination struck in the British Isles, the Triple Unite was as much a propaganda piece for the King as it was a means of meeting the enormous expenditure of the war.

“Despite his Catholic origins, the reverse proclaims his defence of the Protestant religion, English law and the liberty of Parliament.

“Furthermore, having been forced to leave the vast resources of London behind, it proved he still had the authority and financial wherewithal to produce a numismatic masterpiece, made by one of the country’s finest engravers, at his new war headquarters in Oxford.”

Among the Cromwell coins is an extremely fine broad coin worth 20 shillings from 1656, which is expected to sell for up to £20,000.

Other Charles I coins in the sale include a very rare Rebel Money Crown – issued by the Catholic Confederacy of Kilkenny which could fetch between £3,000 and £4,000.

Two unusually shaped, crude-shaped shillings or siege pieces from Carlisle and Pontefract, are estimated to sell for around £12,000 and £6,000 respectively.

Mr Webb said: “Carlisle was defended by the Royalist forces under Sir Thomas Glemham from October 1644 until the following June, when it was surrendered to the commander of the investing Scottish army, David Leslie, later Lord Newark.

“The city was never assaulted, the siege being rather in the nature of a blockade, and the surrender was brought about in part by the scarcity of food, and in part by the hopelessness of relief.”

German-born Gietzelt opened an antique shop on the Frankfurter-Alle in Berlin in 1977 and he started collecting coins after receiving presents from his mother and great-grandfather.