Sex education will become compulsory for in secondary schools, the government is set to announce.

Primary school children are also expected to have lessons on modern relationships.

Sex education is only currently compulsory in local authority run-schools and only includes biology lessons. The new measures will extend to grammar schools, academies and free schools.

Conservative MPs David Burrowes and Maria Miller, the former women and equalities minister, tabled an amendment to the children and social care bill that would introduce relationships education to the national curriculum.

“For the purposes of safeguarding and promoting the welfare of children, the secretary of state must, by regulations, make relationships education a statutory component of the national curriculum within the meaning of part 6 of the Education Act 2002,” the amendment said.

A No 10 spokesman said: “The department will be saying more than this in due course. High quality relationship and sex education is an important part of preparing young people for adult life.