Complicated even more if Catalonia secedes from Spain.

You would hope that whichever political party is in power if Britain ever leaves the EU realise that it would be less expensive to continue to support retired ex-pats already living in other European countries rather having them all return penniless.

Yeah but they would be stuffing themselves if a million to two million needy pensioners turned up back in the UK with no means of support.  Still, since when has any gvernment member worried about anything involving 'ordinary' peole eh?