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The guidance from the Government-backed Human Fertilisation And Embryology Authority, for “trans and non-binary people seeking fertility treatment”, contains a section aimed at prepubescent children. However, critics say the children it addresses are so young they still believe in “Father Christmas, fairies and dragons” and should not be considering “potentially life-changing decisions”. The guidance states: “If you haven’t gone through puberty yet and you’re keen to start hormone therapy or puberty-suppressing medication as soon as possible, it may be possible for you to store your ovarian tissue or testicular tissue, which can be collected via a surgical procedure.”

However, it warns: “These treatments are experimental and there have only been a very small number of resulting live births worldwide following replacement of ovarian tissue.” The guidance forms part of a raft of advice for transgender people wanting to preserve their fertility, including information about using donor sperm or eggs for those about to “undergo genital reconstructive surgery”, or for trans and non-binary people who “find it distressing to come off their hormone therapy”. Supporters say the guidance, to be reviewed next year, will allow children the chance to have a family and avoid puberty with hormone suppressing drugs, whose effects are reversible. They can then take potentially irreversible sex change drugs, which is allowed after the age of 16.

Potentially life-changing decisions like these are beyond the capabilities of primary school children some of whom still believe in Father Christmas, fairies and dragons.

The news has fuelled debate over what some see as the “promotion” of the idea of changing gender among children. Chris McGovern, chairman of the Campaign For Real Education, said: “Potentially life-changing decisions like these are beyond the capabilities of primary school children some of whom still believe in Father Christmas, fairies and dragons. "Adults are foisting their neuroses on children. It is unfair and could have potentially devastating consequences.”

However, Christine Burns, editor of Trans Britain, said: “If you asked a person, ‘Are you in favour of people being able to preserve fertility for example after cancer treatment?’ they would say, ‘of course’. Why should we think any differently when it comes to transgender?” The HFEA also offers advice to freeze eggs, sperm or embryos for those who have not started fertility hormone therapy that can lead to loss of fertility. A spokeswoman said: “After lengthy consultation with a wide range of clinical experts and transgender patients and groups, we developed guidance for trans and non-binary people of all ages, and the clinics treating them. The advice on our website is the direct result of that consultation.”