Pedantry mode on: the phrase “United Kingdom” (with inconsistent capitalisation) was sometimes used to refer to Great Britain before the union with Ireland: it is so used throughout the Parliament of Scotland’s version of the Act of Union, for example (e.g., article 3: “That the United Kingdom of Great Britain be Represented by one and the same Parliament, to be stiled the Parliament of Great Britain.”)
But it doesn’t seem clear whether it was considered an official title or merely a descriptive phrase.
