Ex-Labour MP Zarah Sultana has accused Jeremy Corbyn and other members of a new left-wing party of “baseless attacks” on her character and said she is consulting lawyers.

It follows an email sent to supporters inviting them to sign up for membership of the new party at the cost of £5 a month or £55 a year.

Sultana had posted on social media encouraging people to join and claiming more than 20,000 people had done so.

But ex-Labour leader Corbyn posted a statement signed by four other independent MPs involved in the party in which he claimed the emails were “unauthorised” and said any direct debits set up should be “immediately cancelled”. Corbyn declined to comment on Sultana’s latest claims.

The row over the membership portal has revealed deep splits in the fledgling party, which was launched in July and is due to hold its founding conference in November.

Members will vote on its official name but it is currently using “Your Party” in campaign material.

On Thursday, Sultana described Corbyn and others as running a “sexist boys’ club” and claimed she had been sidelined by other members of the party’s working group.

She said the membership portal was “in line with the road map set out to members”.

The party said it had referred the matter to the UK’s data protection watchdog.

In a statement posted on X on Friday night, Sultana said that “a number of false and defamatory statements have been published about me concerning the launch of Your Party’s membership portal”.

The Coventry South MP said that they were “baseless attacks on my character are politically-motivated and I intend to hold to account those responsible for making them”.

“To that end, I have this evening instructed specialist defamation lawyers,” she added.

Sultana said that at “no point was members’ data misused or put at risk” and that “all funds received from members were ringfenced and protected in the appropriate manner”.