They're almost always British.
Armed response were there within three minutes of the first 999 call and all three attackers had been shot dead within eight minutes. On this occasion, the universal arming of the police would have made no difference.
We can't deport British people, we're not going to ban a religion because of the actions of a handful of nutters, but it's likely that we'll now see an increase in the powers to arrest and hold without charge and a clampdown on hate preaching (something that should have happened long ago).