Parents are pushing children as young as three to change gender without consulting a specialist first, experts have warned.

Some children are starting school with a new name and gender identity after 'socially transitioning' – without teachers having been told.

The NHS's top psychologist for transgender children warned yesterday of a major increase in the trend, saying parents are researching the subject online and taking advice from internet forums and transgender lobby groups.

The warning comes as the latest figures show the number of referrals to England's only specialist clinic for children has almost doubled in four years.

Bernadette Wren, head of clinical psychology at the Tavistock and Portman NHS Foundation Trust which runs the service in London, said parents are researching the subject online and taking advice from internet forums and transgender lobby groups

Last year 2,590 children were referred to the Gender Identity Development Service. Ten were aged three and four, and dozens more were of primary school age.

Bernadette Wren, head of clinical psychology at the Tavistock and Portman NHS Foundation Trust which runs the service in London, said: 'We have had some children who have gone to school and nobody in the school knows.'

Dr Wren cited the example of a five-year-old whose name was changed from Billy to Ellie by his parents because 'he was always at his happiest when he could wear a dress'.

Billy insisted his body was wrong wanted it 'fixed'. Dr Wren said: 'He was deeply unhappy and asked his mother to take him to the doctors to cut his willy off.'

The clinic proposed a 'watchful waiting process' during which the parents were encouraged to help Ellie 'tolerate the reality of the body'.

But the parents acted 'more affirmatively' and the child is formally known as Ellie at school and in other settings and is now 'unequivocally related to as a girl'.

The parents are now waiting for Ellie to turn 12 when they expect the clinic to provide hormone blockers, believing that anything less would be 'unthinkable and cruel'.

Children can be given puberty blockers on the NHS from the age of 12 and sex-change hormones from the age of 16.

Dr Polly Carmichael said that some families put great emphasis on ensuring the correct gender pronouns are applied

Many 'socially transition' at a younger age – but Dr Wren warned that doing so prior to puberty can lead to problems when the child is hit by a 'wall of reality' as their body starts to change.

She said: 'We think that is setting up problems for later. There is no magic solution.

'Some families think the social transition means it is all going to be fine, but it is much more complicated.

'We are anxious that there's some magical thinking that they won't really go through puberty. I'm not condemning these parents, but I think there's much more to learn.'

Dr Polly Carmichael, director of the Gender Identity Development Service, added: 'There are some families where they will talk about it being a hate crime if you get the pronoun wrong with a very young child who has made a social transition.

'There are internet forums where parents talk and, if a parent has a good experience of something, other parents will follow. Parents do want the best for their kids.'

Youngsters sent to the London clinic, or its outreach centres in Leeds and Bristol, are given counselling and around 45 per cent of initial referrals lead to physical treatment such as hormone injections.

The clinic, which has a two-year waiting list, has come under fire for 'rushing' children into potentially irreversible medical treatment.

In April five specialist clinicians resigned over concerns some children had been wrongly diagnosed and sent for life-changing medical intervention without a thorough assessment of the other options.