Sinead O’Connor’s music video for her biggest hit Nothing Compares 2 U was “a distilled, pure potent piece of film” that “connected with millions around the world”, according to the director of a documentary about the late singer.

The Irish star, who has died at the age of 56, was propelled to international fame with the cover of the Prince ballad in 1990.

The video for the single shows a distinctive close-up of her face in a black polo neck, singing straight to the camera as tears roll down her cheeks.

Kathryn Ferguson, who made the documentary Nothing Compares, has described it as “surely one of the most famous videos of all time and will always be”.

She told BBC Breakfast: “I think she sang from the heart. She was incredibly authentic, with all that she did, and I just think it cut through the noise and really reached people in every corner of the world and just had a very profound emotional effect on people.

“And I think that’s what really drew people to her initially. And then I think once she had them there, it was all of it.

“Obviously people adored everything that she wrote and sang, but then when she also started to use her platform to speak out she just became this incredibly potent figure for speaking truth to power and she was really adored and looked up to for that.”

On the power of the video, Ferguson said: “This was the MTV generation with so much happening, and graphics, and there was a lot of bells and whistles in our pop videos at that point.

“And I think just it was such a distilled, pure potent piece of film and it just connected with literally the millions around the world and it’s surely one of the most famous videos of all time and will always be.”

She continued: “I can just speak as an Irish woman and what she’s meant to me and to us.

“She was just this huge icon to all of us, someone that we hugely admired and looked up to.

“And the big reason that I wanted to make the film at all was because of the impact she had on me as a young Irish teenager growing up, and the impact she had and the emotional dent that was left when I and my friends witnessed what then went on to her, happened to her, in the mid 90s and the backlash that she, that she endured.”

O’Connor sparked controversy when she ripped up a picture of Pope John Paul II on US sketch show Saturday Night Live in 1992, in protest at the Catholic church, and the backlash was vitriolic.

She was incredibly authentic, with all that she did, and I just think it cut through the noise and really reached people in every corner of the world and just had a very profound emotional effect on people

Ferguson said: “It was disgraceful. Certainly when you watch the film now people are astounded at the level of backlash and how violent it was against this 25-year-old woman who was just speaking her truth, it’s horrendous what she had to endure.”

Irish broadcaster Dave Fanning said: “Her prescience was unbelievable because she always made bold public statements about child abuse and organised religion.

“She said Vatican was a nest of devils and a lot of people were going ‘What is wrong with this woman?’

“And ten years later, when the Pope came out and said, Well, actually, there’s been a lot of bad things, and in the next 20 years it was ten times even worse, she was 100% correct.

“And she was one of the first types of people that we ever heard say that. And don’t forget in Britain we had cheeky chappy Jimmy Savile with a cigar, nobody knew anything.”