A knife attack on a Taylor Swift dance workshop in Southport left three children dead and eight others seriously injured. The killings then sparked the worst rioting on our streets for more than a decade. Police, mosques and hotels housing asylum seekers were targeted. Terrified residents were barricaded in their homes. The violence was stoked by far-right activists and fuelled by lies and disinformation online. Darragh MacIntyre reports from some of the worst affected towns and cities and asks what can be done to prevent such violence from happening again.