A veteran feminist and opponent of government plans to streamline how people can legally change their gender aims to set up a “new women’s liberation movement” to lobby a future Labour government.

Ruth Serwotka, convener of the Socialist Feminist Network, said she and others on the left had been “frozen out” of voicing their concerns to the party leadership about what they believe would be the impact of the government’s proposed Gender Recognition Act. The act would make it easier for people to self-declare their gender without having to be assessed by clinicians.

Nearly 500 people from Labour, the Greens, the Women’s Equality party and trade unions attended the latest meeting of the group, which took place in London at a location that was kept secret because of what the group alleges is intimidation by trans activists.

“I think that in time there will be an impact on Labour’s support among women and trust in the party from women,” said Serwotka.

Further meetings are planned around the country, she said, and will lead to the establishment of “a new women’s liberation movement” later this year.

“It will talk about wider issues than just transgender issues and really go back to the founding principles of the women’s liberation movement, look at whether they are fit for purpose, and consider what any new founding principles might look like. We want to do that because we certainly want to be able to influence a Labour government.”

The campaign by Serwotka and other feminists comes against the backdrop of divisions in Labour over whether transgender women can be included on all-women shortlists for parliamentary seats. The party is embarking on a consultation after confirming they are welcome to stand without a gender recognition certificate.

Divisions threatened to spill over on Saturday at the annual meeting of an influential group on the party’s left, whose membership includes Jeremy Corbyn and Jon Lansman, the activist currently involved in a separate power struggle to become Labour’s general secretary.

Factions in the bitter split had both been encouraging supporters to join the Campaign for Labour Party Democracy (CLPD), which met in central London.

They include CLPD member Jennifer James, who has established a crowdfunding campaign to bankroll a potential legal challenge in relation to Labour policy on all-women shortlists. The crowdfunder states that the election of self-identifying transwomen as women’s officers and their inclusion on all-women shortlists is reducing and undermining female representation in the party. She was suspended from the party over comments made by her online.

James issued a call for allies to attend the campaign’s annual meeting after a young Labour activist, Max Shanly, called on people to join the group in order to “clear out the transphobes and cranks”. James’s online campaign, which has now raised more than £23,000, has been criticised as “transphobic” with figures such as the MP Clive Lewis supporting trans women being allowed on to all-female shortlists and describing James as “wrong”.

Leigh Drennan, a councillor and vice-chair of Young Labour, said that much of the debate had been marked by what he called “casual transphobia”, and that social media had allowed those opposed to letting trans women on to the shortlists to appear as if they had more support than they actually do.

“I am a gay man and know the battles that have had to be fought over decades to win rights for gay people. That battle has been won in many – though not all – quarters, but it is still going on for trans people, and they need Labour’s support,” he said.

“The vast majority of the public would not care either way about the Labour party’s internal position, but we are the largest political party in western Europe and I think we have got to lead in this.

“I think that the overwhelming majority of the Labour party certainly support the inclusion of trans women on all-women shortlists. In 40 years’ time people will look back and view campaigns for the exclusion of trans women as bizarre.”

The transgender model Munroe Bergdorf was last week appointed as an LGBT adviser to the Labour party, saying on social media that she was “absolutely delighted” to be part of a panel to support the shadow equalities minister, Dawn Butler.

The move was criticised by the Conservatives because of Bergdorf’s previous controversial comments, which she insists were taken out of context by newspapers, that she no longer had the energy to talk about the “racial violence of white people any more”.

Facebook Twitter Pinterest Transgender model Munroe Bergdorf, who has been appointed LBGT adviser to the Labour party. Photograph: Teri Pengilley/The Guardian

• This article was amended on 4 March 2018 to clarify the focus of the crowdfunding campaign set up by Jennifer James.

