An Englishman has British nationality, as does a Scotsman. They both live in the United Kingdom. So domicile becomes less important in the equation. Or does it?
Well, strictly speaking, domicile is actually completely irrelevant as the rules are really designed to designate where you pay tax; I just think that the rules are interesting when applied to your question... they could equally be applied Highlanders as opposed to Lowlanders; Islanders to Mainlanders; Townies to Countryfolk or any other groups you care to contrast.

I accept that there are probably millions of exceptions to the rule!