Sex education in England's primary schools is to be limited to those aged nine and over, with explicit discussions on topics such as contraception to be delayed until the age of 13, according to new guidance to be proposed by the government.

The revised guidance on relationships, sex and health education is expected to be published this week by the education secretary, Gillian Keegan, and is likely to contain further restrictions on teaching about gender and identity, with teachers told to instead explain biological facts, according to reports.

Keegan will announce a consultation that proposes schools be barred from teaching sex education of any type before year 5, when children are nine years old.

A Whitehall source said: Most schools are doing a great job [teaching sex and relationship education], however, there have been many concerning reports, and these limits are based on advice from an expert panel.

Schools would be given the flexibility to discuss topics outside the detailed age groups in certain circumstances, such as if a younger child shared an inappropriate image with a class.

It's never an easy balance to make to ensure children are both prepared but also able to remain children but this guidance achieves that, the source said.