"James VI of Scotland styled himself King of Great Britain"

"He became James I of England when Elizabeth died."

Indeed he did. James VI was also king of England. But the point I was making was that he likd to style himself as King of Great Britain. However that does not mean that a kingdom called Great Britain actually existed at that time outside of the royal imagination. Scotland and England remained seperate kingdoms for a further century (short period of the republican commonwealth aside) until the Kingdom of Great Britain was created in the 18thC.