Pupils must not be allowed to change gender in schools without telling their parents, Rishi Sunak has said.
The Prime Minister told teachers that letting boys identify as girls was 'not a neutral act' and could have a 'significant impact' on children.
He also said school staff must alert parents if their children want to be referred to by different pronouns.
His comments give the strongest indication yet of the likely contents of long-awaited guidance for head teachers on how to handle transgender rights.
It was reported last night that the guidance will finally be published this week, banning schools from letting pupils 'socially transition' by changing their names, pronouns or uniform if their parents do not consent.
Children questioning their gender will even be prevented from playing competitive sport, The Sun claimed.
Schools will be forced to tell parents if students are questioning their gender under new Government guidance to be published this week, according to a report.