The first rule of Secret Cinema used to be simple: don’t talk about Secret Cinema. But my, how the success of this clandestine company, who devise immersive theatrical experiences around film screenings, has got people talking. Indeed, something that only attracted 400 people back in 2007 – with a production of Gus Van Sant’s skater drama Paranoid Park – has now snowballed into an urban phenomenon, with Secret Cinema’s last event enthralling more than 21,000 cinephiles clad in fancy-dress. The secret’s out, it seems.