Actor Cillian Murphy, who played the lead role in Ken Loach’s Palme d’Or-winning film The Wind That Shakes the Barley, talks to the director at the BFI Southbank about a prolific career dedicated to documenting social and political injustice, the importance of artistic collaboration, the often-overlooked humour in Loach’s films, and the impact working with Loach had on his own approach to acting.