it is a little known aspect of ww2 in britain that many people of italian/german...etc heritage were arrested and detained during the war.

it was called defense regulation 18B

https://en.wikipedia.org/wiki/Defence_Regulation_18B

I incidentally found out that Darby Sabini was detained under this law. For anyone who is a fan of the TV show Peaky Blinders, he was the Italian mobster character from the first season.