I would be unhappy if someone was rude to me at check in.

My point is that the comment about a referendum was irrelevant to your argument. The use of the word ‘they’ infers that all Scottish people are as rude as the staff member you describe, which we are not, or at least no more than any other UK citizen. If her behaviour does not appear to be a one off as you suggest (we all have off days) then why did you not complain at the time? If her behaviour concerns you enough I would suggest taking the route suggested by Plunet above iotherwise let it lie. Complaining here will achieve nothing in rectifying the situation for yourself and others.