The gay rights organisation LGB Alliance was set up to “promote transphobic activity rather than pro-LGB activities”, the head of Consortium, an umbrella group of LGBT organisations told a court on Monday.

In the first full day of hearings in the appeal by the transgender rights charity Mermaids against the Charity Commission’s decision to award charitable status to LGB Alliance, Paul Roberts, the chief executive of Consortium, said that LGB Alliance was created to pursue an anti-trans agenda.

In cross-examination, Akua Reindorf QC, for LGB Alliance, repeatedly questioned whether the label transphobic was merited in this case, arguing there were areas where the rights of lesbian, gay and bisexual people might not be aligned with the rights of trans people, justifying the creation of a separate charitable organisation.

The day’s hearing at the General Regulatory Chamber explored the line between transphobia and campaigning for the separate rights of lesbian, gay and bisexual people.

Questions focused on several contested areas of LGBTQ+ rights. At the start of the hearing there was a discussion of the changing definition of sexual orientation. The definition given by the country’s largest LGBTQ+ organisation, Stonewall, has shifted in the past decade from “same-sex attracted” to “same-gender attracted”; LGB Alliance says it was founded to stand up for the rights of same-sex attracted people.

Reindorf asked Roberts: “Do you think it is transphobic to say a person with a female body cannot be a gay man.” Roberts replied: “Yes.”

Reindorf asked if being attracted to people of the same gender was “a qualitatively different thing” to being attracted to people of the same sex. “I don’t believe we live in such a clearcut, binary way,” Roberts replied.

Reindorf also highlighted concerns raised by LGB Alliance that some children who have been referred to gender identity services might otherwise have gone on to be gay, but were offered puberty blockers as treatment for gender dysphoria.

She cited media interviews with Tavistock gender clinic staff warning that possible same-sex attraction was being ignored and noted that some clinicians had said sending children who may be gay down the pathway to change gender felt like “conversion therapy”.

Roberts said there were “elements of transphobia” in that position.

Roberts was asked about questions raised in the Hilary Cass review of gender identity services for children and young people over the 4,400% rise in the number of young girls, a disproportionately high percentage of whom were same-sex attracted, being referred to the service.

“There seems to be an extraordinary sudden rise in same-sex attracted girls identifying as male and seeking a medical pathway. If this is happening, then is it not properly a matter of great concern to an organisation which promotes LGBT rights?” Reindorf asked. Roberts said he was not an expert in this area, but added that in his daily work he saw “many young trans people and many trans adults living healthy lives, and this would not reflect their experiences”.

Roberts was also asked to address the question of whether lesbians should be refused membership of lesbian dating sites if they stated they would refuse to date trans women and to state whether he agreed with comments made by Nancy Kelley, the chief executive of Stonewall, that not wanting to date trans people was “sexual racism”.

He said no one should be coerced to have sex with someone against their will.

In 2020 Consortium refused to admit LGB Alliance to its umbrella group of organisations, of which Mermaids is a member. In skeleton arguments released on Monday, Mermaids said it would argue that LGB Alliance was “not tackling problems facing lesbian, gay and bisexual people, but rather is seeking to prevent the resolution of problems facing transgender persons”.

In its skeleton arguments LGB Alliance said the appeal was ideologically motivated, arising from a “profound disagreement with LGB Alliance’s approach to the promotion and protection of LGB rights”.

It is understood to be the first time one charity has attempted to remove legal status from another. The hearing will continue until Friday.