Chest binding is potential child abuse, the Metropolitan Police has said, as concerns are raised over the actions of a trans charity.
Scotland Yard has said that if police receive reports of a child using a breast binder, which is used to flatten the chest, officers will investigate it along with social services.
It comes after an investigation by The Telegraph found that Mermaids has been discreetly sending binders to children as young as 13 and 14 whose parents will not let them use one.
On its website, the Metropolitan Police describes the offence of "breast ironing (also called breast flattening)", which is a form of female genital mutilation most commonly practiced in Cameroon.
The force describes it as "child abuse" and says that "sometimes, an elastic belt, or binder, is used to stop them from growing".
The description led to questions over how the practice differs from the use of binders on children who believe that they are trans.
Ian Acheson, a former Home Office official and visiting professor at Staffordshire University School of Law, Policing and Forensics, said: "I'm really confused. Is this not 'child abuse' if the same process is advocated by a UK registered charity acting in collusion with a minor against the wishes of parents?"
'Potential child abuse'
According to guidance from the Crown Prosecution Service, breast ironing is an offence "regardless of consent. It is not possible to consent to serious assault".
A Metropolitan Police spokesman told The Telegraph: "The supply of a breast binder on its own is not a criminal offence.
"However, if an individual case of someone using a breast binder or undergoing the practice of breast ironing is reported to police, it would be investigated jointly with social services as potential child abuse. The same approach would be taken regardless of culture or community."
Mermaids has not commented directly on the findings of The Telegraph's investigation, but said it takes a "harm reduction position" that providing a binder and safety guidelines "is preferable to the likely alternative of unsafe practices and/or continued or increasing dysphoria".
Before it offers to send a binder, Mermaids staff alert children to a study by the Johns Hopkins School of Public Health - which found that 97 per cent of adult users experienced health impacts from binding including pain, rib fractures, changes to the spine, headaches, respiratory and skin infections and muscle wasting.
According to the study, the most comprehensive to date: "Commercial binders were the binding method most consistently associated with negative health outcomes, possibly because such binders have the potential to provide more compression than other binding methods."
On Tuesday, Baroness Nicholson of Winterbourne, a Tory peer, said: "I have been following very closely the Mermaids saga with mounting horror that this so-called charity is allowed by our laws to abuse the essential parental responsibility of health and welfare of their children.
"I will be ready to crowdfund myself for a court case if this shocking behaviour is allowed to continue unchecked."
In the wake of The Telegraph's investigation, the Charity Commissions said it was "aware of concerns about Mermaids' service provision and are assessing the information" to determine whether or not it is a matter for the regulator.
Maya Forstater, the co-founder of Sex Matters, said: "We have heard from parents, teachers and therapists who are concerned about the actions of Mermaids and we would encourage them to write directly to the Charity Commission and give evidence of their concerns."