A woman who lost her job after expressing views that sex cannot be changed and transgender women are "not women" has told Sky News she does not regret anything she has done or said.
Maya Forstater lost a test case at an employment tribunal in 2019, arguing that her belief should have legal protection.
The judge ruled her views were "not worthy of respect in a democratic society".
Her appeal is being heard next week and will include an intervention from the Equalities and Human Rights Commission.
In her first broadcast interview, she says that losing her appeal would set a "scary" precedent and that it would be "open season for women in particular, but for anybody who speaks up about women’s sex-based rights".
Ms Forstater is a tax expert and a feminist and is the protagonist in a bitter legal battle about sex, gender and free speech.
She believes the body someone is born with determines their sex, and that sex is immutable and cannot be changed or lost.
These beliefs are seen as at odds with the rights of transgender people and with the opposing view that gender and how someone identifies is of greater importance.
In 2018 she was working as a consultant and a visiting fellow at Washington-based think tank the Centre for Global Development.
In the autumn of that year she posted a number of tweets relating to her beliefs about sex.
These included her opposition to proposed reform of the Gender Recognition Act which would allow trans people to ‘self-identify’, legally transitioning from the gender assigned to them at birth without a medical diagnosis.
This caused a couple of colleagues to complain about her, starting a process which ended in her contract not being renewed.
She took her case to the Central London employment tribunal, arguing her beliefs should be legally protected as ‘philosophical beliefs’ under the 2010 Equality Act.
This would mean someone could not be discriminated against purely for holding them.
"It’s the ability to talk about material reality," says Ms Forstater.
"The reality is there are two sexes. Girls grew up to be women, boys grew up to be men.
"They should be able to wear what they like, call themselves what they like, act however they like, but sex matters.
"Sex matters for healthcare, sex matters for other people’s privacy, it matters for how we understand the world, and it matters in organisations."
But some see these views as deeply transphobic.
The judge at her tribunal ruled against her, describing her views as "absolutist", "not worthy of respect in a democratic society" and "incompatible with human dignity and the fundamental rights of others".
When challenged on the offensive nature of her views, Ms Forstater is keen to stress that she never harassed anybody in the workplace.
Legally and in practice, she says, having the belief protected "doesn’t give you the ability to harass or abuse anybody".
She says her fight is about being able to openly discuss issues of sex and gender. "Employers have to be able to think these things through," she insists, "and we have to be able to talk about them."
Her case has been high profile after the author JK Rowling intervened, tweeting her support with the hashtag #IstandwithMaya.
But her views cause serious offence and distress to many transgender people. Many say they amount to a denial of their right to exist and threaten a healthy and respectful workplace.
"If a person obtains a gender recognition certificate they should have the full protection of the law in exactly the same way we would expect anyone else to have the full protection of the law," says inclusion and diversity consultant Bobbi Pickard.
"If we undermine that, then that fundamentally undermines protections for all trans people in the UK."
"The tweets that she was sending are unacceptable to me personally, they’re deeply offensive to me personally," says Ms Pickard.
"Trans people in this country are being vilified for something that is a natural, hormonal development of the brain in the womb, it’s no different being transgender as it is to having green eyes or brown hair or the colour of your skin."
Whichever side prevails, the appeal will set an important precedent relevant in workplaces and beyond. It will determine whether you can be discriminated against for holding the belief that sex is immutable, even if you never act on it.
Both sides could go to the Court of Appeal if they lose.
Ms Forstater says the journey has been an "isolating" one for her, but when asked if she has any regrets says no.
"I don’t think if I’d said something differently I would have been saved from this," she tells Sky News.