The High Court will rule on a landmark case about whether children who wish to undergo gender reassignment should be prescribed “experimental” puberty blockers and cross-sex hormones.

Keira Bell, a 23-year-old woman who began taking puberty blockers when she was 16 before “detransitioning”, brought legal action against the Tavistock and Portman NHS Trust, which runs the UK’s only gender identity development service for children.

The legal challenge was also brought by Mrs A, the mother of a 16-year-old autistic girl who is currently on the waiting list for treatment.

Puberty blockers court case
Keira Bell has brought legal action against the Tavistock and Portman NHS Trust (Sam Tobin/PA)

At a hearing in October, their lawyers said children going through puberty are “not capable of properly understanding the nature and effects of hormone blockers”.

They argued that there is “a very high likelihood” that children who start taking hormone blockers will later begin taking cross-sex hormones, which they say cause “irreversible changes”.

Ms Bell and Mrs A are asking the High Court to rule it is unlawful for children who wish to undergo gender reassignment to be prescribed hormone blockers without an order from the court that such treatment is in their “best interests”.

But the Tavistock and Portman NHS Trust say the claimants are seeking to “impose a blanket exclusion” on children under the age of 18 being able to consent to medical treatment, which they say is “a radical proposition”.

On Tuesday morning, Dame Victoria Sharp, Lord Justice Lewis and Mrs Justice Lieven will give their ruling on Ms Bell and Mrs A’s legal challenge.

At the hearing in October, Ms Bell and Mrs A’s barrister Jeremy Hyam QC said: “The use of hormone blockers to address gender dysphoria does not have any adequate evidence base to support it.”

He added: “The effect of hormone blockers on the intensity, duration and outcome of adolescent development is largely unknown.

“There is evidence that hormone blockers can have significant side effects, including loss of fertility and sexual function and decreased bone density.”

In a witness statement before the court, Ms Bell said: “I made a brash decision as a teenager, as a lot of teenagers do, trying to find confidence and happiness, except now the rest of my life will be negatively affected.”

She added: “Transition was a very temporary, superficial fix for a very complex identity issue.”

But Fenella Morris QC, representing the Tavistock and Portman NHS Trust, said the use of hormone blockers “has been widely researched and debated for three decades”.

She added: “It is a safe and reversible treatment with a well-established history.”

The High Court’s ruling is expected to be delivered at 10.30am on Tuesday.