Labour leader Jeremy Corbyn praised the late ex-Wham! Singer George Michael for championing LGBT and workers' rights.
Michael fronted a documentary about HIV to coincide with World Aids Day the year he came out. The film, Staying Alive, focused on the experiences of six young people from different countries who were either infected with or affected by the HIV virus.
The singer came out as gay following his arrest in April 1998 for engaging in "a lewd act" in front of an undercover police officer in Beverly Hills. He was given a £500 fine and 80 hours' community service for the incident.
He later said: "I never had a moral problem with being gay."
In a Guardian interview, he revealed: "I'd been out to a lot of people since 19. I wish to God it had happened then. I don't think I would have the same career – my ego might not have been satisfied in some areas – but I think I would have been a happier man."
The music legend was a vocal supporter of the HIV charity the Terrence Higgins Trust. LGBT charity Stonewall tweeted its sadness at the news of his death, writing: "R.I.P. George Michael. You inspired many and your music will live on in the hearts of the community. You will be sorely missed."
Miley Cyrus also paid tribute to the star, writing: "Miss you already! Thank you for your radical activism in the LGBTQ community! Love you always! "
Thames Valley Police said the star's death was "unexplained but not suspicious". His manager Michael Lippman said he received a phone call on Sunday morning telling him that Michael had been found "in bed, lying peacefully".
Lippman told the Hollywood Reporter that there was "no foul play whatsoever", but that Michael's death from heart failure was unexpected.
Funeral plans for the star are expected to be announced later.