This was said to dc1 at school
Apparently he had an argument with someone who then said 'Just go back to your own country!'
When dc1 pointed that Britain IS his country (he was born here, always lived here, hold a British passport), he was then told 'well your my needs to go back to her Ian country then' (I'm the one not British in the family. I'm from another European country. Being living here for 20 years, longer than my 'home' country)
Dc1 was clearly annoyed by the comment but didn't see it as a major issue.
I do wonder though. Is that worth reporting to the school, the same way you would report a racist comment?