Stewart who founded The Pop Group in 1977 as a teenager in Bristol with John Waddington, Simon Underwood, Gareth Sager and Bruce Smith, was described as a "dear friend, fellow agitator and creative force of nature".

"Mark Stewart passed away in the early hours of Friday, 21 April 2023," a statement released by Mute Records said.

He had a "hugely confident and dominating presence" that was coupled with a "warm and sensitive nature".

"Knowing Mark, working with him, laughing with him and thinking with him was like nothing else," the statement from Mute added.

"His hugely confident and dominating presence was coupled with a sensitive, warm, creative, curious, intelligent and hilarious nature - traits that were often hidden upon first meeting this towering tour de force.

"He was always, vocally, on the side of the oppressed, and did all he could to ensure people were treated correctly."

Inspired by punk, dub and reggae, The Pop Group released their debut album, Y, in 1979.

They disbanded the following year after one more album, the provocatively titled For How Much Longer Do We Tolerate Mass Murder?, after a final performance at a Campaign for Nuclear Disarmament rally in Trafalgar Square in 1980.

Stewart began to work with early hip-hop artists such as The Last Poets and members of Sugar Hill Records.

He frequently collaborated with other artists, such as Bobby Gillespie of Primal Scream and trip-hop group Massive Attack's Daddy G.

In 2010, The Pop Group reformed for a series of live performances, and recorded two studio albums.

Stewart's last performance with the band was in the ruins of Coventry Cathedral, for Coventry UK City of Culture 2021.

Tributes have been paid by Daniel Miller, who ran the label Mute which Stewart recorded on, producer Adrian Sherwood, and his former bandmate Sager.

Miller said: "His musical influence has been much greater than is often acknowledged... I can't imagine you being anything other than restless but I hope you find your very special peace."

Sherwood, with whom Stewart collaborated on the 1983 album, Learning To Cope With Cowardice, described him as "the biggest musical influence on my life".

"Mark was the most amazing mind of my generation, RIP," Sager wrote.

"Thank you my brother. You were the biggest musical influence in my life and our extended family will miss you so so much. Love forever," he said.

Massive Attack, also from Bristol, said the city would "never be the same".