Security tried to eject Jeremy Corbyn’s climate change-denying brother from a speech being given by the former Labour leader about the environmental crisis.
Piers Corbyn accused staff at the event in Brighton on Sunday of assault as he refused to be ejected while his associates heckled speakers.
Reports suggested he intervened after the chair of The World Transformed event taking place separately to the Labour Party conference had asked for questions from women and people of colour only.
Piers Corbyn was seen handing out leaflets containing the conspiracy theory that man-made climate change does not exist.
After the event, he turned up at a rally where his brother was due to speak and gave his account of what happened earlier.
Piers Corbyn told the PA news agency: “I attempted to ask a question, they grabbed me and they assaulted me and I shoved back at the person, the security guard, who assaulted me and sat down and refused to leave and stayed in the meeting.
“They tried to remove me and they gave up.”
Asked if he gets on well with his MP brother, Piers Corbyn responded: “Well… most of the time.”
At the later event with Labour left-wingers on Hove Lawns, Piers Corbyn’s crew was received with anger and repeatedly told to “shut up” for shouting over MPs and other speakers with messages criticising coronavirus lockdowns.
A spokesman for The World Transformed said: “Piers Corbyn was admitted to TWT21 this afternoon as with all other ticket holders.
“The climate crisis is real and TWT has a long history of working with climate activists.”
Elsewhere in the main conference hall, white men were urged not to “dominate” speaking slots.
During a debate on housing and transport, the chairman of the session noted the people putting their hands up to contribute did “not reflect the diversity” of those in the hall.
Mark Ferguson, a member of Labour’s National Executive Committee, told delegates in Brighton: “I am afraid, and I am not speaking from a position of particular strength here, there are too many white men putting their hands up.”