Yeah, between them before the police get to them they might kill as many people as die in the UK from road accidents in say.. half an hour? It took two ISIS inspired loons to kill one soldier on the streets of London remember. That's not a great attrition ratio for the terrorists. Same with the 'you ain't no muslim bruv' bloke. You just can't do a lot of harm on the streets of Britain with a carving knife before the police take it off you and throw you in a cell.
Without proper military grade equipment the ability for a single person to kill lots of other people is severely limited. At best you can run amok for a bit and injure maybe a handful of people. Two or three? They might actually get somewhere if there are two or three thousand of them, then they might have some effect in the grand scheme of things. And I doubt there are - we're talking about the extreme edge of the tiny minority.
