The Gregorian calendar was adopted in Britain and Ireland in 1752. It had been adopted in most of mainland Europe 150 years previously. The Gregorian calendar which is called after Pope Gregory XIII is the most widely used international calendar.
Until the adoption of the Gregorian calendar the Julian calendar was in use in Ireland and Britain. The Julian calendar was introduced by the Roman Emperor Julius Caesar in 46 BC. It calculated the year at 365 days and 6 hours. However the actual length of the year is 365 days, five hours, forty-eight minutes, forty six seconds.
During the centuries following the introduction of the Julian calendar the discrepancy led to a slippage of days. Easter for instance was being celebrated later each year. This led Pope Gregory to introduce the new calendar.
By the time the Gregorian calendar was introduced in Great Britain and Ireland in September 1752, in the Julian calendar there was a difference of 12 days. It is reported that people protested at the loss of 12 days from their lives. The Gregorian calendar was not introduced in Greece until 1924, Iran 1925 and Turkey 1926.
The introduction of the Gregorian calendar caused September 2nd to be followed by September 14th in the year 1752 On This Day.
Photo by timatymusic 
Issuing of the Gregorian Calendar