Adult transgender clinics in England are facing a Cass-style inquiry into how they treat patients after whistleblowers raised concerns about the care they provide. NHS England has announced that it is setting up a review of how the seven specialist services operate and deliver care after past and present staff shared misgivings privately during a previous investigation. As a first step, NHS England will send “external quality improvement experts” into each of the clinics to gather evidence about how they care for patients, to help guide the inquiry’s direction. The move follows the publication on Wednesday of a landmark review by Dr Hilary Cass, a former president of the Royal College of Paediatrics and Child Health, which recommended sweeping changes in the way that the health service treats under-18s who are unsure about their gender identity. In a letter responding to Cass’s report, which NHS England sent on Tuesday to the seven trusts that host adult gender dysphoria clinics (GDCs), it told them: “We will be launching a review into the operation and delivery of the adult GDCs, alongside the planned review of the adult gender dysphoria service specification.” NHS sources said that the review would be comparable to Cass’s inquiry. It was prompted by a lack of reliable evidence on key issues involved in the care of children and young people who are questioning their gender identity, such as the safety and efficacy of puberty blockers and cross-sex – masculinising or feminising – hormones. “It will be external, rather than done in-house. It will be led by someone external. It will be fairly similar to what Cass did with children’s services, but this time it will be looking at adult services”, a source said. It could “conceivably” be a senior doctor like Cass. The letter explained that the inquiry was needed because of “concerns put to the [Cass] review team by current and former staff working in the adult gender clinics about clinical practice, particularly in regard to individuals with complex co-presentations and undiagnosed conditions. It was being launched also because there was “an increasing incidence of individuals seeking to ‘detransition’ following previous gender affirming interventions and the absence of a consistent, defined clinical approach for them”, said John Stewart and Prof James Palmer, NHS England’s national director and medical director respectively of specialised commissioning. Mermaids, a charity supporting trans, non-binary and gender-questioning children, welcomed that Cass’s report “recognises the current system is failing trans youth”. But, a spokesperson added: “We are concerned that some of the language in the report is open to misinterpretation and could be used to justify additional barriers to accessing care for some trans young people in the same way the interim report has been.” NHS England also intends to force adult gender dysphoria clinics to hand over data which they refused to share with University of York researchers whom Cass had asked to obtain to help draw up best practice guidelines for how the NHS should help such vulnerable young people. It will outline the health outcomes seen among the 9,000 people who as under-18s were cared for by the gender identity development service at the Tavistock and Portman NHS mental health trust. Six of the seven trusts did not cooperate, prompting Cass to complain in her report that a potentially world-leading research project had been “thwarted” by NHS secrecy. Wes Streeting, the shadow health secretary, said he was “pretty angry” to learn about the blocking tactics. “Under a Labour government there will be accountability for that – you’re not going to get away with it,” he said. In the same letter NHS England made clear to the trusts that if they do not disclose the details, they will resort to “mandatory direction in this respect” to compel them to do so. Concerns raised by whistleblowers in 2018 at the gender identity development service within the Tavistock and Portman NHS foundation trust clinic led to NHS England’s decision to commission the independent Cass review into the services provided to children and young people with gender-related distress. Dr David Bell, a senior psychiatrist and staff governor at the Tavistock, delivered an internal report to the board in 2018, with testimonies from 10 clinicians, warning that the clinic was failing vulnerable children and calling on staff to suspend all hormone treatment for children until there was better outcome evidence. Cass told the Guardian that the “thwarting” of the research project was coordinated and “ideologically driven”. The University of York received “significant opposition from all but one of the adult GDCs including refusal to facilitate the initial opt out stage of the study”, she said. The Devon Partnership mental health trust was the only one of the seven to give York researchers the data. Kate Barker, the chief executive of the LGB Alliance, said it was “deeply troubling that attempts to gather evidence for the Cass review have been deliberately blocked”. Mermaids said it welcomed “calls for more high-quality, transparent research which supports trans children and young people to receive timely, holistic, supportive and personalised care”. Cited reasons for the six trusts’ refusal to cooperate included ethical considerations, although Cass said Health Research Authority approvals had been granted, and resource impacts, although Cass wrote the clinics were “contractually required to take part in research and appropriate costs would have been met by NHS England”. “There was no substantive reason for it. So I can only really conclude that it was because they didn’t feel that it was the right thing to do to try and nail down this data,” she told the Guardian. “They were putting up reasons that didn’t that just didn’t hold water. “Clearly, the trans community is fearful, rightly so, about their rights and about their healthcare. They’ve had a very bad deal in healthcare. I can understand that both they and the people delivering the service will be fearful about anything that might question that. But I think we have to separate the rights of older adults, whom we have more data on and who are at a stable point in their life for making decisions, from younger people who are still in a developmental trajectory.” Robbie de Santos, director of campaigns and human rights at Stonewall, an LGBT rights charity, said: “Gender healthcare for adults in the UK is, simply put, not fit for purpose. Many trans adults are being forced to go private at great personal expense to avoid waiting lists in excess of half a decade. We would welcome a review aimed at tackling this unacceptable state of affairs and building capacity into the system.”