Royal standard of the United Kingdom

The royal standard of the United Kingdom is the banner of arms of the monarch of the United Kingdom, currently Charles III. It consists of the monarch's coat of arms in flag form, and is made up of four quarters containing the arms of the former kingdoms of England, Ireland, and Scotland. There are two versions of the banner, one used in Scotland in which the Scottish quarters take precedence, and one used elsewhere in which the English quarters take precedence.

Source: Wikipedia — Royal standard of the United Kingdom (CC BY-SA 4.0)