When we went to war with Germany in both World Wars all Germans (or of German descent - except for our Royal Family!) living in the UK were rounded up and put in internment camps for the duration of the war.
What do we do now while we are at "war" with ISIS or whatever they are called now, we continue to let people in to this country where we have no idea of their background or intentions.
We are so weak and sloppy with our immigrant controls, but then that goes for most of Europe.