Big-screen documentaries never change the world. Blackfish has not shortened the queues to see maltreated killer whales leap through hoops at SeaWorld. Super Size Me reduced neither the all-American waistline nor the profit margin of McDonald’s. The Cove did not prevent the Japan whale industry slaughtering dolphins. So what possible chance, more than a decade after Michael Moore’s Fahrenheit 9/11, has a mere film of bringing about that most chimerical of holy grails: an admission that the case for invading Iraq was knowingly built on a lie?

We Are Many revisits the anti-war marches of 15 February 2003.