The new guidelines to head teachers are set to be published tomorrow in the UK. It will also spell out for the first time the end of the parents’ right to opt their children out of sex and relationships education classes in secondary school. The change will guarantee all children to receive at least a term of lessons by the time they are 16.

Head teachers will be ordered to bring in the new classes when they are introduced nationally in 2020 following a six-month consultation by the UK Department of Education.

Primary school pupils will learn about same-sex and trans families, as well as staying safe online – and developing “healthy, respectful relationships”. Secondary school pupils will have classes on relationships and sex, including lessons on the ‘catastrophic’ damage caused by female genital mutilation (FGM), and the risks of sexting, online grooming, domestic violence, and forced marriage.

Pupils will be told that FGM is illegal. Since July 2015, a total of 296 FGM protection orders have been made to protect girls at risk. Earlier this month, the mother of a three-year-old girl in east London became the first person to be found guilty of FGM in the UK.

The new curriculum is being brought in on the orders of education secretary, Damian Hinds, which is likely to infuriate thousands of Jewish, Christian and Muslim parents. Earlier this month, in Birmingham, a primary school using five picture books about LGBT+ relationships, including ‘And Tango Makes Three’, about a gay penguin couple bringing up a chick, is already being targeted by hundreds of protesters demanding the lessons to be stopped.

The protesters accused the head teacher of promoting LGBT+ causes without their consent at Parkfield Community School. Some parents, from a mostly Muslim area, said that they would rather leave the country than let their children carry on with the lessons. They held up signs that said: “education, not indoctrination” and “let kids be kids.”

Publication of the guidelines comes as a petition signed by more than 100,000 people objecting to the new curriculum will be debated in the parliament.

The campaigners say that the lessons are vital in protecting children from online child sex exploitation and grooming. Growing numbers of children who think that sending intimate photos is part of a normal relationship – when it is illegal under the age of 18.

Dozens of rabbis have also signed a letter protesting over religious schools having to teach children about “alternative lifestyles”. An academic, Geoffrey Alderman, said ultra-Orthodox Jewish parents were prepared to home-school their children rather than accept the new compulsory classes in schools.

Religious groups that don’t want their children taught about LGBT+ issues insist that teaching children about sexual relations should be left to parents, not teachers.