The Union Jack is a composite of three crosses: St. George's of England, St. Andrew's of Scotland and St. Patrick's of Ireland. The first Union flag, the St. George's Cross over the St. Andrew's Cross, was introduced to ships in 1606. In 1660, the British flag was officially described as the Union Jack. St. Patrick's Cross was added in 1801. In 1933 that the Union jack could be flown on land by any British subject.
The United Kingdom is comprised of England, Scotland, Northern Ireland, and Wales.