By Jack Mendel Police have arrested one man following ‘critical incident’ in Hainault after a sword attack which so far has claimed the life of a 13-year-old boy. Footage circulating on social media showed police responders in a residential area of the north east London area, as other unverified footage showed a man wielding a large blade hiding near houses. The Metropolitan Police said at 9am they were at an incident in the Hainault area and a man had already been arrested. Deputy Assistant Commissioner Ade Adelekan said: “This must have been a terrifying incident for those concerned. “I know…