Gilt
When England became Britain inthe 17th century James the VI of Scotland became James the 1st of England. Which meant he became the first King of Britain.
The first Queen, in her own right, was Anne.
William & Mary reigned together.
OK
Anotheoldgit.
Thank you for your reply which I needed to ascertain an answer in a quiz that I am setting.
I am now going to take the cowards way out by replacing the question.
As always though a question posed in the Answer Bank expands my knowledge.
You could argue that Edward I of England was the first person to style themselves the King of Great Britain, given his aggressive policy towards both Wales and Scotland. Ultimately he lost the war against the Scots but he did claim to be overlord of both England and Scotland. Depends on your point of view.
Certainly James VI and I was the first real one but Ed must have a shout