Britain’s only NHS gender identity service for children is reviewing its operations amid claims made by a senior member of staff that it is failing to examine fully the psychological and social reasons behind young people’s desire to change gender.

The views are shared by a group of parents of transgender children, who have raised their own concerns that the Tavistock Centre’s gender identity development service (GIDS) in London is “fast-tracking” young people into life-altering decisions without fully assessing their personal histories.

In a letter to the trust’s board, seen by the Observer, the parents say they fear “the GIDS team is being asked to engage with and assess complex and difficult cases within a highly constrained time frame”.

They continue: “We have specific concerns about the situation of those with gender dysphoria in the age group 17 to 25 who are referred to the [adult] GIC [gender identity clinic], where they do not receive the complex psychosocial assessment offered at GIDS: for these young adults there is little exploration of the family or cultural context of their still developing gender identity.”

The Tavistock confirmed that a senior member of staff had submitted a report to its board, raising issues about its service. The Observer believes that the report questions whether the clinic should do more to consider young people’s personal histories, notably by examining whether they are on the autistic spectrum, have experienced trauma or are being influenced by social pressures, before helping them on the path to transition. As a result, the clinic has begun an internal review, to see whether these views are shared more broadly by staff.

In a statement, the Tavistock said: “A document has been produced that makes allegations about the service. In response, our medical director is conducting a review of the issues raised. All staff in the service are aware of the review and have been encouraged by both our medical director and chief executive to avail themselves of this opportunity to express their own views about the service.”

With complex cases, we will often extend the time given to trying to understand what may be going on Tavistock and Portman NHS foundation trust

It added: “The trust is concerned by the tone and manner in which these allegations have been made. They reveal a negative attitude to gender dysphoria and gender identity which does not reflect the views or the approach of the trust.”

The parents claim that the huge increase in numbers of children seeking referrals, which has risen from 97 in 2009 to 2,519 in the year to April, is placing great demands on the clinic, with potentially negative consequences for children.

“Given the pressure under which GIDS now works, we believe there is a real danger that the cohort of young people who enter GIDS post-16 may be fast-tracked on to adult services in an attempt to reduce caseloads,” the parents claim. They said they feared the adult service did not adequately examine psychosocial factors that they claim may influence a young person’s decision to transition.

But the Tavistock insisted that “comprehensive psychosocial assessment precedes any referral to the endocrine clinic for consideration of physical treatment”, and that no one was being fast-tracked through its services.

In a statement, it said: “We do not limit or curtail assessments because of pressure to move swiftly to medical interventions. With complex cases, rather than truncating assessments, we will often extend the time given to trying to understand what may be going on. Whilst the national specifications against which the service is commissioned describe an assessment phase of between four and six meetings, one outcome of assessment may be further assessment. Nevertheless, we are always mindful that gender dysphoria is not in and of itself a mental health diagnosis.”

The view that psychosocial factors – such as the popularisation of trans issues on social media, or the role trauma has played in their early life – can help shape someone’s desire to transition is rejected by many trans support groups. They said their experience was that, far from being fast-tracked, adolescents experienced a lengthy assessment process before transitioning could begin.

“The reality we hear from our service users is quite the opposite of the suggestion that services are rushed,” said Lui Asquith of the transgender support charity Mermaids. “In most cases, after the initial assessments and because of the rigorous approach to assessment the Tavi implements, there will be a further long period of ‘watchful waiting’, which can lead to trans children not getting timely support.

“At Mermaids, we see that a delay in necessary, developmentally appropriate or age-specified medical intervention can have a negative effect on the wellbeing of a trans child – an inability to concentrate at school, to engage with their peers, to excel in their hobbies – because they are not getting the support they need in time.”