My passport says The United Kingom of Great Britain and Northern Ireland. .. remove NI from that line and you have The United Kingdom of Great Britain as stated in artical 4 of the Acts of Union. Ireland joined the UK in 1801 but left about 120 years later, so you are playing with words but cannot alter the substance. If either Scotland or England (Wales wasn't a signatory) left, the union would be dissolved so two new states.
On currency, Denmark and the UK had opt outs, Sweden can suit itself as can Bugaria, Czech Republic, Croatia, Lithuania, Hungary, Romania and Poland, who by the way has been in the EU for a number of years and has immediate wish to adopt the Euro.
There are no rules dealing with expulsion of EU members, quite the opposite, look at the state of Ukrain and the EU is desperate for it to join.
Governor Carney made it quite clear that, being independent, the Bank of England would make any arrangement between its members work. Any country going into an arrangement with another would have to cede some of its sovereignty and that applies to England too.He said a currency deal was desirable.
Where do you get the idea that Scotland couldn't affords a health service, education, defence? Read las week' FT where