And the latest rare coins to be uncovered are the 2015 Britannia £2 coins, with around 1 in 200 struck showing the Queen's effigy upside down! According to experts at website Change Checker this means fewer than 3,500 coins are floating around waiting to be found. It's not certain how much the coins will sell for yet, but it's likely to be more than face value. Keep your eyes peeled!