LGB Alliance sought to “undermine” the work of two charities supporting transgender rights, a court was told.

Dr Belinda Bell, the chair of the trustees of Mermaids, said that the charity and Stonewall had been “relentlessly subjected to some of its worst treatment”.

Mermaids, which supports transgender, non-binary and gender diverse children and their families, launched the appeal against the decision of the Charity Commission to grant LGB Alliance legal status last year.

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It is believed to be the first time a charity has sought to remove the status of another charity. The case is being heard at the General Regulatory Chamber in London.

In a statement submitted as part of proceedings, Bell said one of Mermaid’s issues with LGB Alliance was that she believed the organisation “repeatedly focused its efforts on children".

Bell’s statement read: “One of the reasons Mermaids has been especially concerned by LGB Alliance is that, since its foundation, it has repeatedly focused its efforts on children.

“As far as I can tell, LGB Alliance appears to accept that adult trans people exist and that they should be allowed to access gender-affirming healthcare.

“However, based on its public communications, LGB Alliance appears to take the view that trans children do not exist, or that they cannot know they are trans before adulthood.”

In response, Bev Jackson, co-founder of LGB Alliance, submitted to the court: “At present, teens struggling with issues relating to sexual orientation have nowhere to go to discuss same-sex attraction not based on gender identity.

“On the other hand, there are plenty of resources, including Mermaids, for those who are affected by gender identity issues.

“Anti-lesbian prejudice and fear is leading many teens, especially lesbians, to believe that they have ‘gender identity’ issues when they are in fact grappling with their emerging lesbian/gay sexual orientation.”

But Bell’s statement claimed LGB Alliance had sought to “undermine” the work of charities such as Mermaids and Stonewall.

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It read: “A central goal of LGB Alliance is seeking to undermine the work of a wide variety of organisations which it says have promoted trans rights to the detriment of women, children and LGB people.

“After Stonewall, Mermaids has been the second biggest target of its efforts, and we have been relentlessly subjected to some of its worst treatment.

“I have already discussed how LGB Alliance has repeatedly stated in public forums that Mermaids seeks to inappropriately push LGB children into identifying as trans.

“Such allegations are false and harmful to Mermaids’ ongoing work.”

Defending her organisation’s position, Jackson said: “We believe that the LGB rights movement has been largely replaced by the LGBT rights movement, which is governed by the theory that gender identity rather than sex is definitive of what it means to be lesbian, gay or bisexual.

“As far as I understand it, all or nearly all of these organisations now propagate the view that everyone has a gender identity, which should take precedence over biological sex in all areas of public life and in law.

“LGB Alliance rejects this view.

“LGB Alliance maintains, and promotes the view, that sexual orientation is about biological sex.

“To my knowledge we are the only charity for LGB people that does so, whilst there are many charities that adopt the view that sexual orientation is based on gender.”

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Jackson had earlier told the hearing she was concerned about the “consequences for young gay men” due to “matters being conflated as if LGBT was all one thing”.

In a witness statement, Jackson said the organisation shared the view of Harry Potter author JK Rowling that “without sex there is no same-sex attraction”.

The hearing is scheduled to conclude on Friday, when a judge will rule on whether LGB Alliance should maintain its charitable status.