Why the documentary must not be allowed to die

There is a price to pay for filming so bravely. The cameraman, Jorge Muller, was arrested and taken to a torture camp, where he "disappeared" until his grave was found many years later. He was 27. I salute his memory.

In Britain, the pioneering work of John Grierson, Denis Mitchell, Norman Swallow, Richard Cawston and other film-makers in the early 20^th century crossed the great divide of class and presented another country.

They dared put cameras and microphones in front of ordinary Britons and allowed them to talk in their own language.

John Grierson is said by some to have coined the term "documentary". "The drama is on your doorstep," he said in the 1920s, "wherever the slums are, wherever there is malnutrition, wherever there is exploitation and cruelty."

These early British film-makers believed that the documentary should speak from below, not from above: it should be the medium of people, not authority. In other words, it was the blood, sweat and tears of ordinary people that gave us the documentary.

Denis Mitchell was famous for his portraits of a working-class street. "Throughout my career," he said, "I have been absolutely astonished at the quality of people's strength and dignity".

When I read those words, I think of the survivors of Grenfell Tower, most of them still waiting to be re-housed, all of them still waiting for justice, as the cameras move on to the repetitive circus of a royal wedding.

The late David Munro and I made Year Zero: the Silent Death of Cambodia in 1979.

This film broke a silence about a country subjected to more than a decade of bombing and genocide, and its power involved millions of ordinary men, women and children in the rescue of a society on the other side of the world.

Even now, Year Zero puts the lie to the myth that the public doesn't care, or that those who do care eventually fall victim to something called "compassion fatigue".

Year Zerowas watched by an audience greater than the audience of the current, immensely popular British "reality" programme Bake Off. It was shown on mainstream TV in more than 30 countries, but not in the United States, where PBS rejected it outright, fearful, according to an executive, of the reaction of the new Reagan administration.

In Britain and Australia, it was broadcast without advertising – the only time, to my knowledge, this has happened on commercial television.