Image caption Debbie is now being seen at one of the NHS's gender-identity clinics

"This was a mistake that should never have happened… how do I go back to being the Debbie that I was?"

Debbie was born a girl and lived most of her life this way.

But almost two decades ago, aged 44, she sought help to transition from a woman to a man.

Debbie underwent a full female-to-male surgical transition, which included having a phalloplasty - where a penis was constructed from skin on her forearm.

She changed her name to Lee and spent 17 years on testosterone - masculinising hormones that can lead to changes such as more facial hair and more muscle developing.

She believed transitioning would allow her to "become accepted in the world". But now, aged 61, she's detransitioning back to the gender she was assigned at birth.

The number of people openly questioning their gender identity has increased rapidly, with demand for NHS specialist gender-identity services in England - for both children and adults - at an all-time high.

Many who transition to a gender different from the one they were assigned at birth will live happy lives. But BBC News has heard from others who, like Debbie, have reversed the process.

"I was what would be considered a pretty gender-nonconforming child," said Thain, now 40.

"And then there was the fact I was attracted to girls… and I just didn't know anybody who was lesbian."

Image copyright Thain Image caption Thain started to transition in her 20s but decided to stop a couple of years later

Once in her teens, Thain said the growing discomfort she had felt around her identity had convinced her she was transgender.

At 26, Thain sought help from the NHS and was prescribed testosterone. But after two years, she decided to stop taking the hormones and detransition.

"It wasn't until I discovered a community who were affirming to gender nonconforming people, which is the radical feminist community, that I really made the decision to stop," Thain told BBC News.

Charlie Evans, 28, also struggled with her gender identity from a young age. At 15, she started to identify as a boy, shaving her head, binding her breasts and using male pronouns.

She never took testosterone and after several years, went back to identifying as a woman.

She has since set up a support network for detransitioners and said she had been contacted by about 300 people, including some who had surgically transitioned. She admitted she could not verify all their stories.

"Most of us are same-sex attracted," she told BBC News. "Most of us identify as either lesbian or bisexual and a lot of us are autistic."

Charlie said many of these women felt at the time they had sought treatment, "they were not in a state that they were able to give consent [to medically transition] because they felt so unwell with eating disorders or depression".

Image caption Charlie said she was surprised how many people had reached out to her support network for detransitioners

Lui Asquith, from Mermaids, which supports transgender and gender-diverse young people, warned such experiences should not be used to imply the system was lacking rigour or people were being dealt with in a way that "suggests they're being pressured or made into being trans".

"That's incorrect," they said. "You can't make someone be trans."

There is no official data for the number of people who detransition. Some studies have suggested 2%, while others suggest lower. But experts have told BBC News the studies are flawed.

Psychotherapist James Caspian has worked with transgender adults for more than a decade. More recently, he's been contacted by dozens of detransitioners.

"This whole area of transgender medicine is very under researched," he said. But he has spotted certain common themes among the detransitioners he has spoken to.

"Quite a lot of them seem to have had a very negative experience of being female in a female body - sexual harassment, even abuse," he said.

Debbie believes she transitioned as a way of dealing with the sexual abuse she endured as a child.

"I thought I was going to be on a journey to becoming a different person... I'd morph into someone else and leave that traumatised woman completely behind," she said.

But through counselling, she added, it had become apparent "the transition was a way of trying to escape".

Image caption Debbie as a young woman and then after her transition, as Lee

Detransitioning is a controversial topic. Christopher Inglefield, who specialises in transgender surgery, explained why parts of the trans community might be "very nervous" about detransitioning becoming a prominent story.

"Any reversal of that transition starts to make society question the whole transition process in the first place," he said.

And this could lead to people questioning the funding and support for much needed gender services.

"What's really important is to ensure that this experience [of detransitioning] isn't used to pressure other people," said Lui Asquith, from Mermaids.

"It shouldn't be used to tell those who are trans, those that are gender diverse, that they are wrong or different. It's about creating a system that makes everybody feel validated."

The Gender Identity Development Service (Gids) is the only NHS clinic in England that treats under-18s questioning their gender identity.

Children can be offered puberty-blocker drugs, which work on the brain to stop the eventual release of oestrogen or testosterone

Meanwhile, adults can begin transitioning through taking cross-sex hormones.

NHS England said adult patients were required to live for at least a year in their desired gender before they became eligible for surgery.

The Tavistock and Portman NHS Foundation Trust, which runs Gids, said its evidence suggested detransition was "very rare" and it was important not to equate all detransitions with regret.

The trust - which also runs the adult Gender Identity Clinic (GIC) - said those pursuing physical interventions to transition and adults wishing to detransition were offered "psycho-social support" throughout.

But two former Gids clinicians are publicly raising concerns about the support available to this vulnerable group, for the first time.

Anna Hutchinson, part of Gids' senior team from 2013-17, said when patients sought help from professionals, they had expectations about the outcome they wanted.

"Many of them are very clear that they want the medical intervention," she said.

"The people for whom that pathway hasn't worked, in retrospect, will say that what they wished they had was therapy.

"So we've got a bit of a dilemma where perhaps what some of this patient group need may not be what they want at this time."

Detransitioners were a "particularly isolated group of people", she said.

"They're having to self-organise to find help and seek treatment."

Psychotherapist Anastassis Spiliadis, who left Gids last month after four years, said he was worried there was not always a proper assessment of an individual's background.

A Gids assessment "usually comprises of three to six appointments", according to its website.

"I know clinicians who are really thoughtful and really cautious in their approach," Mr Spiliadis said. "But I worry how much actually could be explored by clinicians who believe in a three-session assessment model."

Gids said its clinicians "work thoughtfully on an individual, case-by-case basis".

Mr Spiliadis, who also works privately, said social isolation, depression and anxiety were common among the detransitioners he was treating - some of whom had been seen at Gids - and some had been diagnosed with autism spectrum disorder.

"They used to make sense of all these difficulties through the gendered kind of lens," he said.

The Tavistock and Portman Trust said it expected private clinicians "to liaise with relevant NHS services who may have supported them in the past" to best help each young person.

"All patients with gender dysphoria have extensive access to regular psychotherapy and counselling support," an NHS England official said.

You can watch Newsnight on BBC Two at 22:30 on weekdays. Catch up on iPlayer, subscribe to the programme on YouTube and follow it on Twitter.

Listen to Going back: The people reversing their gender transition, on File on 4, BBC Radio 4 at 20:00 on Tuesday. Listen again here.