When the Olympic games were held in London in 2012, 3 years prior the Royal Mint decided to release a total of 29 50p’s illustrating the 29 different sporting events that would be held at the games.
One of the coins showcased the various aquatic events, the coin was designed to show a swimmer swimming in the water, with the water lines around the swimmers face.
However, some coins were struck incorrectly and showed the lines of water across the swimmers face.
This is an example of one of these coins, which has been graded and authenticated by NGC the coin achieved a MS67 grade which is the highest graded coin. According to the NGC Population guide the population of this coin in this grade is only 1, and this is it.