Perhaps someone should remind Boris Johnson that the original Roman Empire fell to violent barbarian hordes, and so the Dark Ages began.
I dunno. Maybe Boris wants a repeat. After all, the Dark Ages were environmentally friendly. No nasty gasoline engines, or anything like that.
According to the article that's pretty much what he said:
“When the Roman empire fell, it was largely as a result of uncontrolled immigration,” Johnson said in an interview at the G-20 in Italy. “The empire could no longer control its borders, people came in from the east, all over the place, and we went into a dark ages, Europe went into a dark ages that lasted a very long time. The point of that is to say it can happen again. People should not be so conceited as to imagine that history is a one-way ratchet.”