they had decided to go for the highest number - so another King James would be James VII
I don't think that's necessarily official. It was a suggestion first made when Elizabeth came to the throne.
The Queen's full title is Elizabeth the Second, by the Grace of God, of the United Kingdom of Great Britain and Northern Ireland, and of her other Realms and Territories Queen, Head of the Commonwealth, Defender of the Faith.
But you don't actually see the Second or II much in Scotland. For example, the post boxes don't have ER II; they have the crown of Scotland.