Zarah Sultana has boycotted day one of the Your Party Conference over the expulsion of members of left-wing groups.
Ms Sultana co-founded Your Party with Jeremy Corbyn in July, but the new movement has been marred with infighting from the outset.
There was a row on the eve of conference after it emerged members of the Socialist Workers Party (SWP) had been expelled from Your Party, as its rules do not permit dual membership.
But a spokesperson for Ms Sultana branded this a "witch hunt" and said she won't be returning until her speech tomorrow.
She said: "Zarah met members outside the conference and condemned the recent expulsions. This witch hunt is indefensible. We must build a party that welcomes all socialists. She will not be entering the conference hall today."
Members of the SWP argue dual membership should be allowed as the SWP doesn't field election candidates.
Lewis Nieslon, the SWP's national secretary, was expelled on Friday as he was on his way to Liverpool, where the conference is being hosted.
He told Sky News: "With far right Reform UK topping the polls and Starmer paving the way for them, we urgently need a new party that unites the whole left.
"It's wrong for those at the top of Your Party to turn fire on socialists like us who have been key to building Your Party on the ground, and are determined to make it the insurgent, inspiring force it can be."
Members of the socialist organisation Counterfire have also been banned from the conference, Sky News has learned.
Cllr Michael Lavalette, who helped set up Your Party's Preston branch, told Sky News earlier this morning that he was not allowed to enter the venue today.
He said he was told there is intelligence Counterfire was going to be disruptive, which he said is "simply not true".
"Counterfire is a very pro-Your Party organisation so I am not sure where that has come from", he said.
He said it would be interesting to see the alleged intelligence "because I've never said anything disruptive, I've been encouraging people to come".
Purge claims 'false'
Ms Sultana has been advocating for what she calls "maximum member democracy" and believes anyone who is a socialist should be allowed in Your Party even if they are members of other parties.
Her allies see the expulsions as an attempt to purge those supportive of her. There are many grassroots left wing groups who want Your Party to be led by members rather than a single MP, a position Ms Sultana supports.
Those groups have hit out at "nameless faceless bureaucrats" close to Mr Corbyn who they accuse of making decisions without members' consent.
However a Your Party spokesperson said claims of a purge are "false".
They said: "Members of another national political party signed up to Your Party in contravention of clearly-stated membership rules - and these rules were enforced."
They added: "We're focused on hosting a democratic founding conference with thousands of members coming together to debate and decide the big issues. This is politics outside the Westminster mold: from the ground up, not the top down."
Ms Sultana was not due to address the conference today with her speech coming on Sunday afternoon. A source close to her said she was still "very much looking forward to it".
They added that it was an "interesting" choice of programming, giving voting on the party's key issues - including whether dual membership should be allowed - will be closed by the time she gives her keynote address, unlike Mr Corbyn who spoke this morning.
Ms Sultana was not involved in organising the conference and claims she was frozen out of the process.
But those in Mr Corbyn's camp claim she froze herself out when she quit the independent alliance (IA), the group of independent MPs and volunteers close to the former Labour leader, who have been stewarding the party's founding process leading up to the conference this weekend.
Ms Sultana previously accused that group of being a "sexist boys club", in a major row in September that saw her launch an unauthorised membership portal and nearly upended the entire project.
She and Mr Corbyn have since patched things up, but in an interview with Sky News yesterday he declined to say Ms Sultana is a friend.
Mr Corbyn acknowledged "stresses and strains" in the set-up of the party, which has also faced rows over donations and policy positions, saying it had become "a lot better in the last few days and weeks and we're going to get through this weekend".
Asked if they were friends, Mr Corbyn said they were "colleagues in parliament, and we obviously communicate and so on".
The pair appeared at separate events on the eve of the party's inaugural gathering.
(c) Sky News 2025: Your Party co-founder Zarah Sultana refuses to enter group's conference hall
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