Backing Cass’s call for all cases to be treated with “great care and compassion”, he said: “We simply do not know the long-term impacts of medical treatment or social transitioning on them, and we should, therefore, exercise extreme caution.”

The 388-page report took four years to produce amid mounting concern that children are being allowed to change gender in schools and by doctors without question.

Cass, the former president of the Royal College of Paediatrics and Child Health, cautions against hasty decisions while children’s brains are developing, calling for “unhurried, holistic, therapeutic support” for those aged between 17 and 25.

She says doctors are “unable to determine with any certainty which children and young people will go on to have an enduring trans identity”.

Cass adds that “life-changing” decisions must be properly considered in adulthood, noting that brain maturation continues into the mid-20s.

She cautions these people are still at a “vulnerable stage in their journey” and that each of the regional centres recommended in her interim report, which will provide mental health and other support to children who want to change gender, should care for people aged up to 25.

The consultant paediatrician says it is not possible to “know the ‘sweet spot’ when someone becomes settled in their sense of self” but that decisions should not be rushed before an individual becomes a mature adult.

We simply do not know the long-term impacts of medical treatment or social transitioning on them, and we should... exercise extreme caution

British Prime Minister Rishi Sunak following the report’s release.

The younger children were, the more likely they were to change their minds, the report finds.

‘Exceptional’ toxicity of debate

Cass says the “toxicity of the debate is exceptional” and that she had been “criticised” by all sides as she published her report into NHS transgender services.

“There are few other areas of healthcare where professionals are so afraid to openly discuss their views, where people are vilified on social media, and where name-calling echoes the worst bullying behaviour. This must stop,” she urges.

Sunak said the government had already acted swiftly on Cass’s previous call to stop routine use of puberty blockers for those under the age of 16.

“We will continue to ensure we take the right steps to protect young people. The wellbeing and health of children must come first,” the prime minister said.

‘Watershed moment’

Wes Streeting, Labour’s health spokesman, said the report should provide a “watershed moment” for the NHS’s gender identity services.

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He said children’s healthcare should always be led by evidence and children’s welfare be “free from culture wars”.

Implement a ‘pause for under 18s’

In a letter to Cass seen by The Telegraph, London, the NHS has said it will undertake a review, conducted by an external expert, of all its adult gender clinics and has in the meantime instructed them “to implement a pause on offering first appointments to young people below their 18th birthday”.

The letter, written by John Stewart, NHS England’s national director of specialised commissioning, said it would also “review the use of gender-affirming hormones through a process of updated evidence review and public consultation, similar to the rigorous process that was followed to review the use of puberty suppressing hormones”.

Children’s clinics have been overwhelmed by referrals over the past decade, now receiving more than 1600 referrals a year, compared with 50 in 2009.

They treat children experiencing gender incongruence or dysphoria, where they feel they are a different sex to how they were born.

Around 2000 16-year-olds have been sent to adult services because they could not be seen by a children’s clinic because of waiting times.

The Cass review says the adult clinics, of which there are 12 in England, refused to co-operate in its research.

An NHS spokesman said: “NHS England is very grateful to Dr Cass and her team for their comprehensive work on this important review over the past four years.

“The NHS has made significant progress towards establishing a fundamentally different gender service for children and young people – in line with earlier advice by Dr Cass and following extensive public consultation and engagement – by stopping the routine use of puberty-suppressing hormones and opening the first of up to eight new regional centres delivering a different model of care.

“We will set out a full implementation plan following careful consideration of this final report and its recommendations, and the NHS is also bringing forward its systemic review of adult gender services and has written to local NHS leaders to ask them to pause offering first appointments at adult gender clinics to young people below their 18th birthday.”

The Telegraph, London