Paul said: “It is believed that it was stored away many years ago by the vendor’s late husband, whose grandfather fought in the Boer War. She had no idea it was there.”

The chocolate was made by Rowntrees, of York.

Paul said: “It is incidentally some of the most controversial chocolate ever made, a Royal commission that triggered a row involving all of the country’s most famous chocolate makers.

“The Queen had decided to cheer up her troops fighting in the war – which was going rather badly at the time – by personally paying for a seasonal gift tin of chocolate to be sent to every ordinary soldier.

“In the end the three firms decided they would make the chocolate and donate it free of charge, but it would be unbranded and in tins that did not carry their names.

“The firms backed down again, sort of. Some of the chocolate was then marked, but the tins never were.”

Although the tins were unmarked, Cadbury, Fry and Rowntree used different firms to make them and there are slight differences between the three.

Rowntree’s tins were made by Mansfield’s Barringer, Wallis and Manners, which later became Metal Box.