Liz Truss has said that schools should not allow children to change their gender identity.
Speaking to The Times, the former prime minister said that allowing children to choose their gender identity, pronouns, and name was "not a neutral act".
The government has promised to bring in new guidance but its publication has been repeatedly delayed.
Truss said the delay was "leaving schools in limbo" and "allowing misinformation to spread".
She called on the government to "press ahead" with publishing new guidance that tells schools they "should be clear about biological sex and not officially sanction social transitioning".
"This delay is leaving schools in limbo and allowing misinformation to spread. There needs to be clarity about biological sex in school, particularly for toilets and changing areas, which should be single-sex spaces," she said.
She said that changing gender identity "should not be officially sanctioned before a young adult has the full decision-making capability to understand the consequences at the age of 18".
"I do not believe that this contravenes the Equality Act but if there are any legal issues, the government should legislate," she added.
Truss shared her views with the newspaper after it was reported last week that Prime Minister Rishi Sunak has backed away from passing legislation to ban the social transition of children in schools.
