Nobody has yet convinced me that there is one "correct" definition of Britishness. A pragmatic (re)definition would be easy, but given the emotions mentioned by Allan and others, the word seems burnt. Until further notice, you will be punished with the name "UK citizens", whenever a clear-cut notion is required. (As for dominions, Channel Islands, Gibraltar, and whatever other constructs you have devised, stick them up your legalistic arsenal ;).)

When Scotland becomes independent, there will be a chance to rethink the whole notion of nation and national identity altogether. The idea of a cozy little England, ditto Scotland, Wales, etc., and a strong European Parliament (at the expense of the European Commission) may appear more and more attractive.