At the Barbican in London tonight, Russian conductor Valery Gergiev will lead the London Symphony Orchestra (LSO) in a performance of Berlioz's The Damnation of Faust, which tells the story of a person who makes a pact with the devil. Some critics see parallels with Gergiev's relationship with the autocratic Russian leader, Vladimir Putin. His name appears on a list of celebrity Putin supporters, according to the Moscow Times, and in the runup to the last Russian election, he publicly stated that he was voting for Putin. In return, his loyalty to the Russian president has been rewarded with personal honours, including the esteemed Hero of Labour, and multi-million state grants for his pet projects, most notably the restoration of his Mariinsky Theatre in St Petersburg.

The audience arriving at tonight's performance by Gergiev will be greeted by human rights protesters holding sparklers, including myself, with the message: "Sparkle for freedom in Russia. Putin suppresses, we sparkle." We condemn Gergiev's support for Putin's repressive regime, his defence of Russia's anti-gay law and his condemnation of Pussy Riot. Gergiev is a great conductor but he colludes with an authoritarian leader and shows little respect for freedom and equality.

Last Thursday, I interrupted the opening night of Gergiev's new LSO season at the Barbican, criticising his pro-Putin stance. I dressed in a tuxedo to look official and the ruse worked: just before the performance began I strode on stage unhindered. Security staff and the audience seemed to assume I was an LSO spokesman making an official announcement.

In a 60-second statement, I told the audience: "Valery Gergiev is a friend, ally and supporter of the Russian tyrant Vladimir Putin … I ask you to oppose tyranny and show your support for the Russian people." Then I was quickly manhandled off stage by security staff before voluntarily walking out of the concert hall, to the sound of applause – some of the audience may have been applauding my eviction but others seemed genuinely supportive of what I had said.

Tonight's follow-up protest takes place on the 96th anniversary of the 1917 Russian revolution. As Putin takes the country backwards to autocracy, Russia needs a new, non-violent democratic revolution. As well as escalating repression against the lesbian, gay, bisexual and transgender (LGBT) community, civil liberties and dissidents are under attack. Peaceful protesters and opposition leaders, such as Alexei Navalny and the Arctic 30, are arrested on trumped-up charges, in a bid to intimidate and silence Putin's critics. His regime has incarcerated political prisoners, including Pussy Riot's Nadezhda Tolokonnikova, in jails that resemble gulags.

Gergiev endorses Putin, despite this shameful repression. That's why we need to protest – to show him and other prominent Russians that supporting an intolerant regime will result in public condemnation and reputational damage.

In response to the protests, Gergiev yesterday issued a public statement in his defence: "I do not discriminate against anyone, gay or otherwise, and never have done, and as head of the Mariinsky Theatre this is our policy. It is wrong to suggest that I have ever supported anti-gay legislation and in all my work I have upheld equal rights for all people."

While his affirmation of personal non-discrimination is commendable, Gergiev's statement does not renounce his support for Putin, whose regime does discriminate against gay people. Moreover, contrary to his protestations, he has defended Russia's anti-gay law, reportedly claiming that it is solely concerned with stopping paedophilia. The Dutch newspaper Volkskrant quoted him as stating: "In Russia we do everything we can to protect children from paedophiles. This law is not about homosexuality, it targets paedophilia."

This misrepresentation of homophobic legislation and blurring of homosexuality and child sex abuse crosses a red line. In addition, by making a public statement that focuses solely on gay rights, Gergiev has misread our objections. We are concerned about more than homophobic persecution in Russia. We also oppose his support for a president who has presided over a much wider suppression of democracy and human rights.

Gergiev's defence is: "I am an artist … This is my focus as a conductor, musician, artist and as artistic and general director of the Mariinsky Theatre and principal conductor of the London Symphony Orchestra." Nice try. The fact is that Gergiev is more than an artist. He chose to be political by endorsing Putin. He must now face the music.