2022 silver 5 pound mule
Following the death of Queen Elizabeth II, the Royal Mint struck a number of commemorative coins, including silver £2 and £5 proofs. The silver £5 reverse was a young and old portrait of Queen Elizabeth II with ELIZABETH REGINA above and 1926 - 2022 below; the silver £2 had a single old portrait of Queen Elizabeth II surrounded by the legend ELIZABETH REGINA 1926 - 2022. Both coins had a portrait of King Charles III on the obverse: the £5 had the legend CHARLES III • D • G • REX • F • D • 5 POUNDS • 2022 • and the the £2 had the legend CHARLES III • D • G • REX • F • D • 2 POUNDS • 2022 •
The £2 and £5 are both the same diameter and during production, the £2 obverse die was accidentally used to strike at least one £5 - an easy mistake to make given the identical diameter and almost identical obverse legend.
The mule was apparently spotted by NGC when grading a 2022 £5 and so far only a single example is known (Rivera, Discovery of the first known Mule of the Royal Mint's commemorative coin honoring the life and legacy of the late Queen Elizabeth II in Coin News, August 2023).