Caz Coronel was standing in the queue for the ladies’ at the Royal Festival Hall on London’s South Bank when she registered a male voice shouting across the vestibule: “The men’s toilets are on this side!”

At first the composer and producer paid little attention, until the man – whom Coronel describes as tall and in his late 60s – approached and touched her shoulder.

He continued to challenge her about being in the wrong queue until she asked him bluntly: “Do you want to see my tits?”

“It sounds funny, but at the time I was shocked,” she said. At that moment, another woman, who Coronel presumes was the man’s wife, ushered him away.

“I have short hair and don’t mind if people think I look male. I’ve often been called ‘Sir’ but when they see my face they either apologise or ask me politely what I like to be called. But I’ve never had anyone approach me before in such a publicly aggressive way.”

“What then flashed through my mind was: Is this what this ruling has done?”

Since the supreme court’s ruling on biological sex, debate around its practical application has focused heavily on access to women’s toilet and changing facilities – in particular after initial advice on implementation from the equalities watchdog, the Equality and Human Rights Commission, amounted to a blanket ban on trans people using toilets of their lived gender, which many say in effect excludes them from public spaces.

Critics of the ruling have suggested it may likewise affect cis women who do not adhere to a straight, white template of femininity.

Support groups report some early indications that gender non-confirming women are facing increased challenges, raising wider questions about how women read each other’s bodies and whether women’s toilets have ever been entirely safe spaces.

Claire Prihartini, who had a bilateral mastectomy, was challenged by a woman in the changing room of her local pool. Photograph: Alicia Canter/The Guardian

Others say these anxieties amount to scaremongering from those who do not agree with the judgment of the supreme court.

Claire Prihartini was diagnosed with breast cancer a year and a half ago. “I had a really lucky experience: I found out early, opted for a bilateral mastectomy and didn’t need further treatment.” Her chest is now flat, with two small scars and no nipples.

Last month, Prihartini was in the women’s changing room area of her local pool. “I was standing with my top off in front of the mirror putting on my swimming cap. Another woman walked in, gasped audibly and said: ‘There’s a man in here!’ I said: ‘Oh I’m not a man …’ in a friendly way, then she said aggressively: ‘You look like a man, there aren’t meant to be men in here’ and continued to look at my body. I didn’t want to engage with her any further so I just walked off into the pool.”

Prihartini, whose experience was first shared on social media by her husband, Jolyon Maugham, founder of the Good Law Project, is at pains to make clear that this was not “a massively traumatic experience”. After she walked away the other woman did not continue to challenge her. Like Coronel, however, she links the incident directly to the supreme court ruling.

“It shocked me that someone felt empowered in the moment to question someone else’s gender so rudely, that it’s becoming normalised.”

While many of the non-conforming women the Guardian spoke to said being challenged in women’s spaces was by no means a new phenomenon for them, they added that they had identified an escalation since April’s ruling.

“People who might have given me a look prior to the judgment have got quite bold in recent months,” says Dee, who did not want to give her second name. Dee was recently challenged by another woman in the changing rooms at Marks & Spencer, before unzipping her jacket to reveal her chest. “She began to apologise but then she said: ‘Well, you should be careful these days.’ She seemed to mean: how dare I appear masculine?”

Taranjit Chana of Black and Brown Rainbow, a grassroots anti-violence service, says their helpline has seen an increase in calls from black and Asian LGBTQ+ people who fear or have experienced challenge in toilets.

“Women’s toilets have never felt entirely safe for black and brown women, because we don’t fit that binary way of looking. In some communities, facial hair is part of who we are, but in public toilets people stare and feel it is acceptable to make remarks because we don’t fit a narrow, European version of female.”

Bridget Symonds, director of services at the LGBTQ+ anti-abuse charity Galop, said: “Galop has seen a significant increase in trans+ and gender diverse people coming to our frontline services for hate crime support. We’ve seen instances where LGBT+ people are being challenged and verbally abused when attempting to access toilets in public spaces, such as pubs. We’re hearing from cisgender lesbians who have been questioned about their gender in public toilets, something happening even before the ruling.”

But some suggest these concerns are being overplayed. Jenny Willmott, co-founder of Scottish Lesbians, another gender critical group that intervened in support of the For Women Scotland case, says she has been challenged in women’s toilets since she was a teenager.

Willmott explains: “I’m the best part of 6ft4in, short hair, don’t wear makeup or skirts. Barely a week goes by that I don’t get a double-take. Women glance in, see a 6ft body with short hair and think: ‘Aah!’. But after the second glance they think ‘Oh OK, it’s a woman.’”

For Willmott, “it’s just something that happens. It used to bother me because we do need to broaden the bandwidth of what a biological woman looks like”.

Other women’s experience of challenge is less straightforward. Nikki Lucas, who has short hair and usually wears a cap along with a shirt and trousers, says: “If you’re masculine presenting or butch lesbian, women’s toilets are not a safe space. I’ve been spat on, screamed at and it’s just so sad that this looks likely to get worse.

“The looks of hate, the feeling that you just don’t know if you’re going to be safe, have really got worse since the ruling, to the extent I now either ask a friend to come in with me or use the disabled toilet, which I feel bad about because it’s preventing them from accessing it.”

Coronel shared her Royal Festival Hall experience on social media afterwards: “I’ve had so many messages from trans women who’ve lived fully as women, used women’s facilities for 20 years or more, who are now scared that they’ll be asked to prove themselves. It’s really awful.”

“Now, more than ever, we need kindness and compassion and a genuine effort to understand each other, even towards those with prejudice.”