October 1969, the 50p joined the 5p (shilling) and 10p (florin) coins in
circulation. It was introduced to circulate alongside its equivalent; the
ten shilling note. The reverse design of Britannia by Christopher Ironside
was traditional, but the heptagonical shape of the coin was revolutionary
and at the time was the only such coin in circulation in the world. The
edges were rounded to ensure that the distance across the coin was a
constant 30mm so vending machines would accept them.