Sam FrancisPolitical reporter
Ex-Labour MP Zarah Sultana has accused Jeremy Corbyn of overseeing a "sexist boys' club" locking women out of the founding of a new left-wing party the pair announced earlier this year.
In a statement on social media, Sultana said she had been sidelined by other members of the party's working group - despite an agreement that she and Corbyn would jointly authorise key steps.
He comments come after Your Party supporters got an email on Tuesday offering £55 memberships only for Corbyn to later dismisses it as "unauthorised" - telling supporters he was seeking legal advice.
Sultana said she had launched the membership website "in line with the road map" set out by the party officials.
Before her statement, Sultana had been posting on social media throughout the morning encouraging people to sign up at cost of £55 for full membership.
Sultana had claimed more than 20,000 people had signed up - meaning the new party could have raised more than £1m in a single morning.
In her statement she said: "My sole motivation has been to safeguard the grassroots involvement that is essential to building this party.
"Unfortunately, I have been subjected to what can only be described as a sexist boys' club: I have been treated appallingly and excluded completely.
"They have refused to allow any other women with voting rights on the Working Group, blocking the gender-balanced committee that both Jeremy and I signed up to."
Before Sultana's comments, Corbyn put out a conflicting statement signed by Ayoub Khan, Adnan Hussain, Iqbal Mohamed and Shockat Adam - members of the Independent Alliance of MPs who are founding the new party. Sultana's name was conspicuously missing from the list.
The statement supporters on Wednesday morning that an "unauthorised email" had been sent promoting a membership portal under a new domain name.
They urged backers to ignore the message and cancel any direct debits that may have been set up.
Sultana defended her decision to set up the membership portal, insisting it was "in line with the roadmap set out to members on Monday and is a safe, secure, legitimate portal for the party".
She claimed she had set up the site to allow supporters to "continue to engage and organise", and that membership funds were held by a company set up by the party to safeguard money until November's founding conference.
Sultana also went on to raise concerns that long-time Corbyn ally Karie Murphy and her associates had been handed "sole financial control of members' money and sole constitutional control over our conference".
She called for Corbyn to publish all party structures arguing only transparency would "restore hope for our members, and ensure nothing like this can ever happen again".
"This party is bigger than any one person," she said, "and we owe it to the movement to uphold its democratic and socialist foundations."
The row is the latest falling out at the top of the new group that has yet to be named or hold an annual conference.
In July, has announced she is resigning from the party, saying she will be founding a new party with Corbyn. A move that took Corbyn and others involved in the project by surprise.
Despite the bumpy start the party began to build momentum, signing up more than 600,000 supporters - under the placeholder name of Your Party.
Earlier this week, Your Party emailed supporters saying membership would open by the end of September and draft party rules and policy positions would soon be published.
This would be followed by national assembles in October and an online vote on the new name for the party.
In November, the party's founding conference will be held.