In June last year, I sat in the writers’ room for Blue Lights season four, reading a Facebook page in which people were listing their house number and ethnicity, in the hope that their homes would not be burnt down. A few days before, in Ballymena, County Antrim, two Romanian teenagers were arrested on suspicion of the rape of a local teenage girl. Those charges were dropped five months later, but at the time the incident was sufficient to strike a match.