Health secretary Wes Streeting has called on the Conservatives to maintain the “cross party consensus” on gender identity services built before the last election in a letter to Kemi Badenoch.

Streeting wrote to opposition leader on Friday urging her to “take the heat and the ideology” out of debate amid controversy over a puberty blocker trial for children.

Both parties committed to implementing the recommendations of a report by leading paediatrician Hilary Cass, focused on gender identity services for under 18s in England, published in April 2024 when the Conservatives were in government. Cass recommended a puberty blocker trial as part of a wider research programme and supported a more “holistic” approach to care.

However, Badenoch and the shadow health secretary, Stuart Andrew, wrote to Streeting on 25 November, saying they were “concerned” NHS England was supporting a clinical trial involving drugs which halted natural puberty.

Cass found “remarkably weak” evidence the drugs were effective in treating gender-related distress, adding there is “no good evidence” on long-term outcomes.

She has said a trial is “the only way forward” in the attempt to understand if there are beneficial effects. The government has since banned the treatment for children outside clinical trials.

The new trial will study the effects of puberty blockers on more than 200 children presenting with gender identity conditions as part of a wider research project on possible treatment pathways. The £10.7m study is being carried out by researchers at King’s College London.

Streeting’s intervention came despite admitting he is “deeply uncomfortable” about medication which affects “a natural part of our human development”.

Puberty blockers stop the body from producing certain hormones, including oestrogen and testosterone. They were traditionally prescribed to children who entered puberty too early, but were later given to young people diagnosed with gender dysphoria and incongruence.

Badenoch and Andrew told Streeting the trial was based on the “discredited, yet still seemingly entrenched, belief in some quarters that a child can be ‘born in the wrong body’ or go through the ‘wrong’ puberty and a normal puberty can be ‘paused’ without causing irreparable harm to children”. They cited infertility and loss of sexual function as possible side effects.

Streeting expressed his own doubts about the trial in an LBC interview on Friday. “There’s something about the opposition to this. Medication that delays or indeed stops a natural part of our human development, which is puberty, I am deeply uncomfortable with,” he said.

However, he added that he planned to follow clinical advice to go ahead with the trial, saying: “It’s gone through rounds and rounds of ethical approvals to approve this kind of study. So that’s the basis on which we are proceeding.”

In responding to Badenoch and Andrew, Streeting said some children were going to “great lengths” to source puberty blockers despite the ban and that gender incongruence is a “real and internationally recognised disorder”, but added the condition was distinct from “girls and boys experimenting with gender norms, which for many children is a normal part of growing up”.

He said: “Only a clinical trial (and longer term follow up) can isolate which outcomes can be ascribed to these treatments, supporting evidence-based decisions for future care.”

Streeting added “cross party consensus” on the Cass review when it was published last year was “a key moment for taking some of the heat out of what is an extremely sensitive issue without stifling debate, where the wellbeing and safety of children must remain paramount.”

He said: “Dr Cass said, on publishing her review, that ‘toxic, ideological and polarised public debate has made the work of the Review significantly harder’ and it will hamper the research that is essential to finding a way forward.

“It is incumbent on us as public representatives to take the heat and the ideology out of this issue, and make sure that children’s health is always led by evidence and medical expertise.”

Badenoch and Andrewsaid in their letter to Streeting that the trial would have no proper control group “creating obvious bias”.

In his reply, Streeting said this was incorrect and said a group of young people not in receipt of puberty blockers would also be studied by researchers. He said these children would be “compared with trial participants with respect to outcomes.”