[iconoclast]

Actually, on British passports today we are billed as 'British citizens', the EU having deemed 'British subject', i.e. subject of Her Majesty the Queen, to be a bit medieval. Technically, if I'm not mistaken, British sovereignty still lies not in the people but where it has long lain: in Parliament (or, more technically still, in the Queen in Parliament, or whatever the anachronistic expression is).

As to N. Ireland, where I happen to come from, I suppose everyone's technically a British citizen regardless of their politics, but as Tdol points out, it's a dodgy issue (let's not start on Scottish or Welsh nationalism, either). Luckily for N. Ireland Nationalists who wish not to have to travel on a British passport, the Republic of Ireland has long awarded Irish nationality to anyone who could prove they had a parent or grandparent born in pre-Partition Ireland (i.e. before 1922), or to anyone who had a parent who was already an Irish citizen - I believe they've tightened the rules a little recently, but you get the idea. So, a fair whack of N. Ireland's population today, including myself, are still entitled to an Irish passport should we wish, and presumably the Nationalists among us have been exercised their entitlement for years.