A landmark judgment that children under the age of 16 considering gender reassignment are unlikely to be mature enough to give informed consent to be prescribed puberty-blocking drugs undermined their entitlement to make decisions for themselves and was based on “partisan expert evidence”, the court of appeal has heard. Tavistock and Portman NHS trust, which runs NHS England’s only gender identity development service for children, is challenging a high court ruling last year in a case brought against the service by Keira Bell, a 24-year-old woman who began taking puberty blockers when she was 16 before detransitioning. The other applicant was the unnamed mother of a teenage autistic girl on the waiting list for treatment. The three high court judges also said the doctors of teenagers under 18 may need to consult the courts for authorisation for medical intervention. As a result of the decision, the Tavistock suspended new referrals for puberty blockers and cross-sex hormones for the under-16s. On Wednesday, in written submissions to the court of appeal, the Tavistock’s legal team, led by Fenella Morris QC, said the high court “countered the statutory presumption of the ability of young people aged 16 and 17 to consent to medical treatment … undermined the entitlement of children under the age of 16 to make decisions for themselves when they have been assessed individually as competent to do so by their treating clinician” and “intruded into the realm of decisions agreed upon by doctors, patients and their parents, where the court had not previously gone”. It said the decision meant that children with gender dysphoria seeking treatment with puberty blockers were “treated differently from others in their age group seeking medical treatment”. Morris said the expert evidence provided by the respondents was “partisan” and had been accepted by the court, even though it had been “given by those without relevant experience, untested, and contrary to that advanced by the appellant”. As an example it cited Prof Neil Evans, “whose post is in a veterinary school and whose key experience in the field is the study of the endocrine systems of sheep”. Morris also said that the court had reached an incorrect decision in holding that the treatment of gender dysphoria with puberty blockers was experimental, arguing that there was more than 20 years’ evidence of their effectiveness. But the respondents’ legal team, led by Jeremy Hyam QC, said puberty blockers were “a controversial and ‘quite possibly unique’ experimental treatment about which there are many uncertainties”. In written submissions, the lawyers said this view was supported by an evidence review of puberty blockers published by the National Institute for Health and Care Excellence on 11 March. Hyam said the high court judges “did not ‘rely’ on the impugned evidence for the purposes of determining the issues but by way of background and context to the decision they had to make”. He said the court’s judgment “in no way departs from the long-established principle that ‘a child who is capable of appreciating fully the nature and consequences of a particular operation or of particular treatment can give an effective consent.’ “The judgment simply sets out the salient facts that a child must understand, retain and weigh up in order to be deemed capable in law of appreciating fully the nature and consequences” of a puberty blockers treatment for gender dysphoria. The hearing is expected to last two days, with judgment at a later date.