When we had our place in Spain (thankfully sold about 6 years ago), We had friends from all over the UK & Ireland. The Spanish called us all English, but nobody cared. However, the identity of say, Scots upon leaving the UK finding themselves in foreign parts is somewhat puzzling. The same goes for Britons living in Scotland. It's OK saying they would be welcome to stay wherever they are, but what will be their official status?
Scotland for instance will become a 3rd nation as far as the EU is concerned with no connection, not even a trade agreement with the EU, how will their nationals fare in say, Spain? How will my sister who is English, long term resident in Scotland, with no official residency, fare? There are problems in Spain since Brexit concerning the status of British Ex-pats even though there are agreements in existence with the EU over medical care etc. How will Scots fare when the (British) NHS can no longer be relied upon to fund their care even though those Scots may be resident in what is still the rump of Britain? Will the English NHS expect the Scottish NHS to pick up the tab for unnaturalised Scots' medical treatment in English hospitals? Would Scots living in England have to take English citizenship to qualify for benefits? That takes 5 years, plus an exam an oath of allegiance to the crown and a ceremony. Since Scotland would be a foreign country, could Scots resident in England Use British passports or apply for new Scottish ones and a residential visa for England?
I am sure there are dozens more questions so far unasked, and many more unanswered.
Mike.X