Billy Porter, Ian McKellen, Sam Smith, Jade Thirlwall, Leigh-Anne Pinnock at London Pride

Billy Porter, Ian McKellen, Sam Smith, and Little Mix members Jade Thirlwall and Leigh-Anne Pinnock were among the celebrities that came out for London's LGBT Pride.

According to LGBT blog Metro, McKellen, Smith, Thirlwall and Pinnock marched in Saturday's parade, with Thirlwall and Pinnock joining transgender children's charity Mermaids.

"Their visible support of trans kids means the world to so many young transgender people and their families," Mermaids tweeted.

Organizers said this year's Pride was its biggest and most inclusive yet. UK daily the Guardian reported that about 300,000 people took part in the official parade through central London and 1.5 million people were in attendance.

From the parade, former England rugby player James Haskell told the BBC: "It's 2019, sexuality shouldn't be an issue."

Porter, the star of Kinky Boots and the FX drama Pose, performed on Saturday in Trafalgar Square.

Asked by UK LGBT glossy Attitude what Pride means to him, Porter replied: "Pride has always been a place where I come for energy, to be re-energized. I came out in the 80s. We were going through the AIDS crisis and Pride was a protest. Pride was community. ...And Pride reminds me that it's the people that make a difference. It's the people that create change."

London Pride began as a protest march in 1972. This year it celebrated the 50th anniversary of the Stonewall riots in New York, which are widely credited with sparking the modern LGBT rights movement.