The terms were first written down by James VI, soon after he took over the throne of England and Ireland in 1603. More than anybody, he was keen to unite his two kingdoms. In his very first speech to the English Parliament in 1604 he made reference to union:
"I am the Husband and the whole Isle is my lawfull Wife; I hope therefore no man will be so unreasonable as to think that I that am a Christian King under the Gospel should be a polygamist and husband to two wives."But the English Parliament saw no advantage in union. The attitude had not changed even a century later. "He who marries a beggar," said Edward Seymour MP of Scotland in 1700, "can only expect a louse for her portion." However a brief window of opportunity opened when England involved itself in a continental war in 1701. Scots had been wanting trade with the English Empire, and now England wanted to close a potential northern front in its war with France. Thus, through mutual expediency, Scotland and England were dissolved - and a new state formed, Great Britain.
At first the union wasn't popular. But from the mid 18th century, the Scottish establishment and intelligentsia threw their weight behind the British state. An unfortunate but seemingly necessary element in embracing a new British identity was to erase the Scottish one. The phrase used for this new identity was not Scottish, but North British. A concept invented by Scots, this was to contrast with the new name for England - South Britain.
But there was a problem - the English. Why should they become South Britons, when England's institutions were effectively unchanged? And the Scots, the people who wanted this change, were unpopular in London. They were hoovering up positions of influence and then recommending their North British friends for further advancement. When a Scottish petition came before the House of Commons, polemicist John Wilkes MP refused to even consider it, saying "I care not who prevails! It is only Goth against Goth!" The reaction against increasing Scottish influence in empire, state and business culminated in anti-Scottish riots at the end of the 1760s. For their own protection, Scots were forced to drink together in Scottish-owned taverns, increasing their clannishness and alienation further. In the face of this rejection, the concept of South Britain survived no further south than Edinburgh.
It is a historical irony that Scotland was saved from becoming North Britain. Not, as a layman might assume, through any patriotic Scottish efforts, but as a result of English indifference to project Britain, and hostility towards the concept of losing their English identity. Even today, many English people habitually talk of England when they mean the UK. It's common for Scots to get annoyed at this casual conflation of the two. Perhaps instead we should be glad. For in never quite fully embracing the South British identity, the English allowed space for the concept of Scotland to live on - despite the best efforts of some Scots to the contrary.