Some primary schools are being forced by local authorities to teach sex education to their pupils, a report has claimed.
The research, published on Monday, raises concerns over the "considerable level of inconsistency" across the country. Many local authorities are incorrectly informing primary schools in their area they will not be eligible for the 'Healthy School' status if they did not teach sex education, it suggested.
The National Healthy Schools programme was introduced by Labour in 1999, but a survey of the 152 local authorities in England revealed inconsistency in the way its guidelines were being interpreted and applied in schools.
Education bodies are forcing schools to impose "liberal and permissive" teaching on pupils warned the Family Education Trust, who conducted the survey.
The trust believes the programme is being used as a "vehicle" to impose sex education on primary schools pupils. According to the report, titled 'Unhealthy Confusion', some authorities are taking an "overly prescriptive" approach and insisting on policies which are not required either by law or the healthy schools criteria to be taught in schools.
Family Education Trust director Norman Wells described the revelations as "very concerning".
"Primary schools that make a principled decision not to teach sex education after consultation with parents should not be stigmatised and denied a sought-after reward for that reason. There is nothing inherently 'unhealthy' about a primary school that decides not to teach sex education."
But the report also highlighted the refusal of some local authorities to adequately inform secondary school pupils about safe sex.
The report concluded there was "considerable confusion and ignorance" among local authorities about the extent to which condoms provide protection against sexually transmitted infections. Some authorities were described by the charity as being "unaware of the considerable limitations of condoms and vastly overstating their effectiveness".
The publication condemned the local authorities which considered it "inappropriate" to inform pupils of the limitations of condoms.
It concluded: "This policy runs the risk of placing some pupils at increased risk of contracting a sexually transmitted infection where they decide to embark on a sexual relationship on the basis of a false understanding they will be safe provided they use a condom."
Sarah, who attended a grammar school in Berkshire, told the Huffington Post UK her year received "barely any" advice on sex education.
"The boys and the girls were split into two classes and we were told if you didn't use a condom you could get pregnant, and that was when we were in Year 10. That was about it really. I found out about STIs from a rather embarrassing- but very necessary- talk from my parents. The issue definitely needs addressing."
Norman Wells added: "It is deeply disturbing to find so much confusion and ignorance about the extent to which condoms provide protection.
"It is ironic that in some local authority areas, the Healthy Schools Programme is undermining the healthiest messages of all", he added.
The report's release coincides with World Contraception Day, which takes place every year on September 26. Figures released by the International Planned Parenthood Federation showed the proportion of young people admitting to having had unprotected sex with a new partner has risen.
A study of British 16 to 19-year-olds has shown 43 per cent of those sexually active admitted to having sex with a new partner without using contraception compared to 36 per cent in 2009. And only 55 per cent of girls said they considered themselves to be "very well-informed" about all the contraceptive options available.