Fifty-five people were arrested on the day of the royal wedding last year, 30 of them for a potential breach of the peace. A year on, 15 of them are taking the police to court for a judicial review to challenge the tactics that were used that day against a 'hypothetical protest that had already been criminalised'. They tell the Guardian why they want the law to change and discuss what the practice could mean for the policing of protests at the Olympics