The man who heckled Jeremy Corbyn at a Momentum rally on Wednesday evening is a Liberal Democrat activist who stood for the party in last month's London Assembly elections.
Zack Polanski told BuzzFeed News he decided to interrupt the meeting of Corbyn supporters because the Labour leader's "passivity and ambivalence for Europe" had contributed to Britain voting to leave the EU in last week's referendum.
Several hundred pro-Corbyn activists gathered at the impromptu meeting outside the School of Oriental and African Studies to listen to the Labour leader ahead of an expected leadership election.
Towards the end of the speech Polanski interrupted by shouting, "What about Europe? What about Europe, Jeremy? Where were you when we needed you?"
Dissenters in the Corbyn crowd: "What about Europe Jeremy - Where were you when we needed you?" "Oh f*** off".
The rest of the crowd reacted very angrily to the heckle, with one man stood in the crowd next to BuzzFeed News shouting, "You Tory heckler! You piece of shit!"
But Corbyn responded by telling the crowd to respect the heckler and insisting "let our friend stay".
Despite this, supporters of the Labour leader were unhappy with the media for subsequently focusing on the then-unknown heckler during evening news bulletins.
The only bit of this evening's Corbyn speech that made the edit on BBC News was the heckle.
@DylanStrain See ITV & BBC report of lone heckle tonight at Corbyn & see media clearly as part of the coup.
It now turns out the individual at the event was not a Labour supporter but Lib Dem Polanski, who stood for the London Assembly constituency of Barnet and Camden in May.
"I did it because as much as Boris Johnson is to blame for the mess we're now in, Corbyn's passivity and ambivalence for Europe means he must take his share of the responsibility too," Polanski told BuzzFeed News. "He was stood on a platform championing the freedom of movement and ironically the freedom of protest whilst I felt at the time he was more concerned about his own political future."
Polanski said he hoped Corbyn would have done his bit for the Remain campaign. "I don't think you can talk about principled collaborative politics but then refuse to share a platform with other party leaders."