“I’m trying to be a walking piece of political art,” said actor Billy Porter ahead of headlining London Pride. “Just as a human being, as an out black gay Christian man, my very existence is political.”

The star of Kinky Boots and TV series Pose performed to thousands in Trafalgar Square on Saturday at what organisers claimed was the biggest, most inclusive Pride yet. About 30,000 people from more than 600 groups took part in the official parade through central London, which was attended by an estimated 1.5 million people.

Porter suggested that concerns from Peter Tatchell and others that the event was being “pinkwashed” and hijacked by commercial interests had been overblown. “The commercial aspect of it is a result of how successful it’s been,” he told the BBC. “And when there’s a version of commercial that’s good … we always have to find the balance in these things.”

Rainbow flags and banners lined the streets in celebration of what began as a protest march in London in 1972 and which this year marked 50 years since the Stonewall riots in New York that gave birth to the modern Pride movement.

The parade was opened by the mayor of London Sadiq Khan, who attacked Boris Johnson for using homophobic language in a 1998 column in which the Tory leadership frontrunner wrote that gay men were “tank-topped bumboys”.

Facebook Twitter Pinterest Revellers at the parade. Organisers say this year’s event is the most inclusive to date. Photograph: Tristan Fewings/Getty

“You’ve got the next prime minister using homophobic language,” Khan said. “When you speak to members of the LGBTQ+ community, they will tell you that some of the homophobia they suffered, the attackers used this language, the same sort of language he’s used.”

No 10 Downing Street was given a rainbow makeover by London Flower School which erected a floral arch over the door flanked by two signs reading “Love is Love”. MPs including shadow education minister Angela Rayner and defence secretary Penny Mordaunt were among the marchers.

In response to demands made by Extinction Rebellion, Pride in London joined the movement in declaring a climate emergency and pledged to make the event carbon neutral by 2020. Activists put up “alternative ads” along the route questioning why the Home Office, the Metropolitan police and corporations were able to participate in Pride, while “marginalised groups are left watching on the sidelines because they are unable to afford spaces on the march”.

Following controversy last year, which prompted Pride in London to apologise after anti-transgender campaigners forced their way to the front of the parade, organisers were keen to stress that inclusivity and representation were a priority this year. A World Area stage to “celebrate diversity … and increase the visibility of black, Asian and ethnic minority LGBT+ people” was erected in Soho. Having boycotted the event last year, LGBTQ equality charity Stonewall were also back at the parade partnering with UK Black Pride and trans rights charity Mermaids.