Scotland didn’t sign the act of union Scottish members of its Parliament did without the sovereign consent of the people.
The English people did not give their consent to the union in any way that we would understand in modern terms, either. It was culmination of a deal which started at the Restoration (of a Scottish dynasty) and continued in the ‘Glorious Revolution.’
This was a sweetheart deal whereby the old aristocratic rich and the new merchant rich said “let’s not have another Civil War, but instead unite against roundhead radicals, Levellers and the like.” So they did, and Anglo-Saxon capitalism was born.
The Scottish aristos and merchants were dead keen to join them in this enterprise of robbing the people (a move which was accelerated by gambling on Darien and losing) and did so in 1707.
Since then the radical cause (or the left) has shared a common enemy north and south of the border.
Which is why nationalism is a defeatist distraction.