Row: A judge has decided a 12-year-old girl can have a sex change against her father's wishes (picture posed by models)

A huge ethical row has erupted over a judge's decision to allow a 12- year-old girl to have a sex change that will turn her into a teenage boy.

The child's father, who is separated from her mother, is outraged at the prospect but despite his objections the taxpayer-funded sex swap has already got under way.

His daughter, who cannot be named because of her age, is already having hormone treatment in Australia in what is one of the first such cases involving a child so young.

The girl has also been given permission to apply for a new birth certificate, passport and medical card in a boy's name.

Last night, a relative of the child claimed the girl had been 'vindictively brainwashed' by her mother into making the decision to have the change.

A cousin who stayed with the girl's family for two and a half years said yesterday that after a bitter break-up the mother had used the child to 'get back' at the father.

'She's been brainwashed from an early age,' said the cousin, who has to remain anonymous to protect the Victorian girl's identity.

'The mother drilled into the girl from an early age that she would have preferred a boy.'

Now the father, who considers his daughter is far too young to make a decision on her gender, is appealing to Melbourne's legal fraternity for help in fighting the case after he ran out of money to afford representation in opposing the sex swap request.

The Victorian Family Court was told that the girl had always considered herself a boy and was at risk of self harm if she continued to develop into a woman.

Hormones now being implanted under the 12-year-old's skin every three months will stop her from developing from a child into a woman, including preventing her hips and breasts from growing.

A further court application must be lodged in coming years for testosterone treatment to deepen the girl's voice and promote growth of facial hair and muscles.

Surgery to remove her womb or ovaries or build an artificial male sex organ must wait until she is at least 18.

The court was told that the hormone therapy was reversible and would give the family 'breathing time' with progressive sex change treatments and operations requiring further court orders.

'I question how reversible the treatment is,' said the cousin. 'There will be psychological consequences that are not reversible.

'I don't think the side effects have been adequately considered. How people treat her will have an effect.

'She will never have this time in her life again.'

News of the judge's decision to grant the sex-change treatment has sparked furious debate.

Medical ethicist Dr Nicholas Tonti-Filippini described the ruling as 'astounding'.

He added: 'I fail to see how it can be in the interests of a young girl to undergo treatment that will change her for the rest of her life.