To one side the 3 3/4in (9cm) high beaker - possibly made by Wedgwood - carries a black printed half-length portrait of the monarch together with military insignia and a map of Cuba.
To the other is the slogan King and Constitution, first noted around 1793 at the time of the outbreak of war with Revolutionary France.
It is a great rarity but was damaged with clever restoration and repainting across the portrait bust likely concealing a substantial crack or break.
There were knowledgeable dealers and collectors who considered it correctly pitched at £800-1200 but - reaffirming the old adage that an item sold at auction is worth only what two people are prepared to pay for it - two specialists competed it to £2800.
