A woman who claims she was given 'experimental' puberty-blocking drugs at 16 without being warned of the consequences is set to lead as a witness in a landmark case.

The Tavistock and Portman NHS Trust, which runs the UK's first gender clinic in London, is being sued over concerns it gave powerful drugs to children as young as 12 without proper consent.

Keira Bell, 23, started gender reassignment at the clinic when she was a teenager after she felt suicidal and asked to be called by a boy's name at school.

She was prescribed hormone blockers to halt the development of her female body after just three one-hour appointments.

But Ms Bell has now stopped transitioning and argues staff did not challenge her want to become a teenage boy.

Keira Bell, 23, (pictured outside the Royal Courts of Justice in January) started gender reassignment at the clinic when she was just 16 after she felt suicidal and asked to be called by a boy's name at school

Ms Bell is now waiting to see if she has fertility issues following the drugs and claims she should not have been rushed into treatment because children cannot given adequate consent.

The judge in the landmark case, Mr Justice Supperstone, told The Sunday Times it was 'plainly arguable' the clinic was acting unlawfully and has given permission for the high-profile trial in the divisional by July.

Ms Bell hopes the case will bring attention to the fact children are given treatment without being properly informed of the lifelong consequences.

'I am constantly taken for a boy,' she previously said in an interview with the Daily Mail. 'I get called "Sir" when I speak to officials. I worry what women think when they see me using their loos or changing rooms.

Ms Bell (pictured in January) is now waiting to see if she has fertility issues following the drugs and claims she should not have been rushed into treatment

'I am living in a world where I do not fit in as a male or as a female. I am stuck between the two sexes.'

Put on what she calls a 'roller coaster' journey, she was given the male hormone testosterone to change her appearance after going to the clinic at 16. Three years ago, she had her breasts removed, in an operation paid for by the NHS.

Despite that dramatic step, Ms Bell has now changed her mind about her gender and is trying to reverse the process.

The Tavistock and Portman NHS Trust, which runs the UK's first gender clinic in London, is being sued over concerns it gave powerful drugs to children as young as 12 without proper consent

Barrister Jeremy Hyam QC said Ms Bell 'underwent the treatment that is in issue in the proceedings'. He added she 'very seriously regrets the process and feels that the way it was handled and her involvement in it was not appropriate'.

At the Tavistock clinic, Ms Bell said there was 'no resistance' to her want to be a boy, even though she was little more than a child and had only just started having periods.

'The Tavistock gave me hormone blockers to stop my female development. It was like turning off a tap,' she said.

'I had symptoms similar to the menopause when a woman's hormones drop. I had hot flushes, I found it difficult to sleep, my sex drive disappeared. I was given calcium tablets because my bones weakened.'

Ms Bell claims she was not warned by the Tavistock therapists of the dreadful symptoms ahead. 'My female hormones had been flushing through my body and, suddenly, a curtain came down on them. It felt pretty bad,' she recalls.

At the Tavistock, Ms Bell (pictured outside the Royal Courts of Justice in January) says, there was 'no resistance' to her want to be a boy, even though she was little more than a child

Campaigners supporting Ms Bell's court battle say the number of young people regretting a sex change is rising.

A new charity, The Detransition Advocacy Network, has been set up to help them. Its founder Charlie Evans was born female but lived as a man for nearly a decade before accepting her birth sex.

She says she has been contacted by 'hundreds of young adults' — some only 19 or 20 — who claim the treatment has not solved their problems.

The Government has also launched an inquiry into the explosion in the number of children wanting to change sex.

In 2009/10, 40 girls under 18 were referred to doctors for gender treatment in England.

By 2017/18, the number had soared to 1,806. Over the same period, annual referrals for boys increased from 57 to 713.

Tavistock and Portman NHS Foundation Trust said: 'We welcome the opportunity to talk about the service and to stand up for our dedicated staff who put the best interests of the young people and families at the heart of their practice.'