I think we should. They came here with the belief that they could live here.
I suppose the argument is that Spain and France may not show compassion to British citizens who have emigrated. Certainly Spain may well be tempted to use it as leverage to gain sovernity of Gibraltar. I think the chances of the French being vindictive is less.
If Scotland leaves the uk and joins the EU could there be an arrangement where ex pats become Scottish citizens? (Even if they are 100% English or Welsh) in the event of British citizens being sent back?