What is the meaning of life? That was the question a pair of New Yorkers, Jeffrey Azize 22, and his 29-year-old brother Cliff, put to orphans of Peru, the homeless on the streets of New York and the lepers they met in the jungles of Ghana.

Later, they brought the same question to a neuroscientist from Stanford Medical Center, the niece of Martin Luther King, the founder of a worldwide arts movement, a Catholic priest and a rabbi.

The result, an award-winning feature-length documentary called The Human Experience, is being screened tonight for the first time in the UK. Cherie Blair is attending the premiere in Leicester Square.

The idea for the film was prompted by the 9/11 bombing of the twin towers, New York. “I was on the second day of an internship with the video network at Merrill Lynch, right across the street from the North tower,” explains Charles Kinnane, 26, the film’s director.

He was staying at St Francis House, Brooklyn, a refuge for young men from impoverished backgrounds, which is run by Joe Campo, the founder of Grassroots productions, an independent film company set up in 2001.

“Joe said to me “let’s make a film when the dust settles,” recalls Kinnane, who had begun to have dinner time conversations about the point of life, with the Azize brothers, long-term residents at the refuge.

“We wanted to talk to people who were living in worse conditions than we do,” explained Michael Campo, the scriptwriter and associate producer. “The purpose of the film is to see why other people who are really struggling, have a happiness, a lightness and a joy that we don’t. Why is this?”

“It was a paradox” agreed Kinnane. “The people we met who had nothing were completely happy.”

In February 2007, the entire Grassroots crew lived homeless on the streets of New York for a week, for the first stage of filming. They say they were astonished by the generosity of New Yorkers. On their last day on the streets, for instance, Kinnane visited Starbucks to beg for coffee.

“The guy at the first counter ignored me,” he said. “But then I said “We’ve been homeless for a week, it’s cold outside.’ The guy at the next counter said ‘have whatever you want.’ I was getting sugar and felt a tap on my back. It was him: he gave me a $5 dollar bill and said “go get some food.”

“We learnt how generous people become when they think less of themselves and more of others,” said Azize. "What moved me the most was the fact we met people willing to tell their life story to total strangers.”

He is in the UK to take questions and answers, along with Campo and Kinnane, after the film’s screening, tonight and tomorrow in the Prince Charles Cinema, Leicester Square. Afterwards the team will take the film, now on its second European tour, to Wales and then Dublin.

So far The Human Experience has won five awards, including the Golden Palm Grand Jury Prize 2009 at the International Mexican Film Festival.

Grassroots are currently looking for a distributor for The Human Experience.