UK flag: how the "Union Jack"" evolved"
September 18, 2014 - The Union Jack is a composite of the flags of England and Scotland, plus Ireland’s cross of St Patrick, adopted prior to Irish Home Rule.
In 1603, King James VI of Scotland inherited the crown of England and became King James I of England. At this point, although both kingdoms had the same king, they remained separate sovereign states with their own parliaments, judiciary, and laws.
In 1606, the King ordered a Union Flag to combine the Scottish Cross of St Andrew with England's Cross of St George. According to the Flag Institute, over the following years the Union Flag became known colloquially as the Jack or the King's Jack, the term jack being a diminutive derived from the term for a small flag flown from the bow of a vessel to indicate its nationality. By 1674, the flag was officially recognised by the term Union Jack.
In 1707, the parliaments were united to form the Parliament of Great Britain, based at the Palace of Westminster in London. In 1801, the Kingdom of Great Britain united with the neighbouring Kingdom of Ireland.
(The Cross of St Andrew is also known as the Saltire - the term saltire being a heraldic symbol in the form of a diagonal cross.)