Almost two years since Russia launched its full scale war in Ukraine – we speak to a man who witnessed and recorded some of the worst brutality of the war. The AP journalist Mstyslav Chernov, together with two colleagues, arrived in Mariupol just an hour before the invasion.

He began filming and didn’t stop for three weeks, telling the story in the Oscar nominated documentary, 20 Days in Mariupol. Channel 4 News was one of many broadcasters who used his footage from inside the besieged city and we should warn you, our interview with him does contain some very distressing images – we began by asking him how difficult it was to watch those images again?