RARELY has a documentary arrived in British cinemas having made the sort of impact in America that I Am Not Your Negro has created since it debuted at the Toronto International Film Festival last September.

Raoul Peck’s documentary, which is based on the writings of the novelist and essayist James Baldwin, was nominated for an Oscar for Best Documentary Feature and has a clutch of awards, starting with the People’s Choice Award at Toronto. It has pulled in more than $6.6 million at the US box office. Critics have described it as a “mesmerising cinematic experience” and a “cinematic séance”. And Madonna has described it as a “masterpiece. Poetic. Brutal. Inspiring.”

But it is at a more personal, individual level that the extraordinary power of the documentary lies.

Peck acknowledges that he has had “several incredible moments” at various screenings. “People standing in the audience during a Q+A and saying not only ‘thank you’ but crying and saying ‘the film has just changed my life’,” he says. “I have seen young black and young white girls standing, everybody saying about their own life and saying this will change everything for them. I never had that kind of situation, whether with my films or with other people’s films.

“We have seen many different generations finding themselves in the film. Because that’s what it does to you: it forces you to think about your own life, how do you see your life, how do to see other people’s, who are different, how do you see your role in society. Those are really very personal questions for any human being”.

The documentary, which had its first screenings in the UK two days ago [Fri], is based on an unfinished Baldwin manuscript, Remember This House. It was to have been his story of America through the lives of three civil-rights leaders whom he knew, but who were all assassinated in the turbulent 1960s: Medgar Evers, Martin Luther King Jr and Malcolm X. However, he never got beyond 30 pages of notes.

The film makes captivating use not only of Baldwin’s written words (voiced hypnotically well by Samuel L Jackson) but of archive images too. We see and hear directly from Baldwin and his friends; there is archive and contemporary footage of civil rights protests and unrest, and police brutality. There are clips from old Hollywood films that speak to how black people were portrayed on the cinema screen. With Baldwin’s penetrating intellect to the fore, it is not difficult to see why it has had such a positive impact at countless screenings across America.

The Chicago Defender newspaper spoke for many in the US when it described I Am Not Your Negro as an “incendiary” film, a “radical, up-to-the-minute examination of race in America”, and a “journey into black history that connects the past of the civil rights movement to the present of #Black Lives Matter”.

One line of Baldwin’s, uttered in a television interview, remains genuinely revelatory. There were days, he question, “how you are going to communicate to the vast, heedless, unthinking, cruel white majority that you are here”. He was “terrified at the moral apathy, the death of the heart which is happening in my country. These people have deluded themselves for so long that they really don’t think I’m human … And this means that they have become, in themselves, moral monsters”.

“He has a lot of those lines,” says Peck. “That’s why I tell people, you don’t just read Baldwin, you study Baldwin. Because each of these lines, each word of the line is a whole philosophy, and sends you looking for more, trying to understand all the metaphors as well that he has included. And, yes, this line about the ‘vast, heedless, cruel white majority’ - I mean, he is making it up as he is speaking. And that’s an incredible capacity, to be able to do that.

“I remember, going back, taking my old Baldwin books when I was preparing for my research, I would find those books totally underlined from the first page to the last page. That’s rare that you can underline almost every line of every paragraph – because it’s like pure philosophy, pure human knowledge, experience, and also poetry, and love, and so many different things.”

Peck, who was born in Haiti and moved with his family to the Democratic Republic of Congo at the age of eight, first encountered Baldwin’s works as a teenager. And Baldwin has remained with him ever since. “Baldwin was the first person who I thought was speaking to me and also speaking about the current world I was living in. He was bringing a very critical analysis and a very progressive one. Automatically, I became drawn to that, and he stayed a compass for me all my life”.

He says he has been taken aback by the way people have reacted to the film in the States.

“I know that Baldwin can get that kind of reaction, but what I discovered through all these screenings is that people go through a very personal, intimate experience watching the film.

“It’s not a film that you can just watch from the outside with a very cynical mind. He causes you to be serious with yourself, to take yourself seriously and to take your life seriously.

“It’s almost like – I don’t know if you’re religious, but you’re sitting in front of your pastor, or a priest, and it’s a confessional relationship, very intimate. You can’t escape, and the person in front of you has credibility, and you don’t feel threatened, although he’s telling you a very strong argument.

“You don’t feel threatened: you just have to swallow it, and think. He is forcing you to think, and not just in an intellectual way, but in a very personal, intimate way. [Baldwin] is looking at you, he’s looking at the camera. This is a very rare experience”.

Among the contemporary footage in the documentary are scenes from such places as Ferguson, Missouri, where the police shooting of an unarmed teenager, Michael Brown, in August 2014 helped give rise to the powerful Black Lives Matter movement. It is not hard to see why many see the film as a powerful exploration of what it means to be black in America today, or why Baldwin’s words have continued to resonate.

Little wonder then that Peck believes that Baldwin is once again necessary. Speaking on Channel 4 News earlier this week, he said: “I felt the rise of stupidity, the rise of ignorance, and there was the need for that voice, that basically changed my life.”

Asked what Baldwin, who died in 1987, would have made of Donald Trump’s America, he said: “I think he would stop sleeping. It’s a very tough situation today, but again, it’s not just the United States. We have seen all over Europe as well. We forget that we had Berlusconi in Italy. This is what democracy has become.

“It’s a matter of celebrity. There is a lot of ignorance, and people want easy answer when we are living in a very complex world, and that’s the time for populists”.

• I Am Not Your Negro is now on show at UK cinemas, including the Glasgow Film Theatre until April 13. www.iamnotyournegrofilm.com/home