Why would they need rescuing if the banks in Spain fail? They moved there of their own free will and should accept any consequences for that decision, it's not like Spain or Portugal are going to descend into civil war which would put the lives of ex-pats at risk.
So you think people should be rescued by the Navy because they can't get their sangria money out of the bank. Not quite the same as being invaded by a foreign power or living in a country that has descended in to civil war is it?
In what way are ex-pats "our own"? Haven't they decided to stop contributing to the UK? Using the Navy to assist a foreign nation in a crisis might generate some international goodwill, I doubt that pitching up to rescue a select few would do that.
I do not object to rescuing ex-pats BTW. I just do not count an ex-pat as British.