The earliest form of the flag of Great Britain was developed in 1606. It displayed a red cross of England superimposed on the white cross
and blue field from the Scotland flag. Because in heraldry a red on blue is not considered permissible, the red cross had to be bordered with white, its own correct field.
Known as the Union Jack is the most important of all British flags and is flown by representatives of the United Kingdom all the world over.
In certain authorized military, naval, royal, and other uses, the Union Jack may be incorporated into another flag. For example, it forms the canton of both the British Blue Ensign and the British Red Ensign. It is also part of the flags of such Commonwealth nations, Australian Flag, New Zealand Flag, and a whole lot more.