The group says young people need to know about the risks of sex

In a letter to the Times newspaper, the Terrence Higgins Trust, the NSPCC and the National Union of Teachers said all pupils were "entitled to" such lessons.

Children needed to know about health risks and where to get advice, it said.

Ministers said schools were teaching about sex and that teenage pregnancy rates were the lowest for 20 years.

The call from the group of charities and other organisations comes after a study found almost half of young people had not been taught about teenage pregnancy.

No school should be able to opt out of delivering good sex and relationships education to their pupils

Letter to the Times

The UK Youth Parliament survey in the summer also found the same number of young people did not know where to find their local sexual health clinic.

The letter to the Times says these figures go "some way to explaining" the disproportionately high rates of teenage pregnancy and sexually transmitted infections in Britain.

Nick Partridge, chief executive of the Terrence Higgins Trust, Dame Mary Marsh, chief executive of the NSPCC, Steve Sinnott, general secretary of the National Union of Teachers, Kevin Barron, chairman of the House of Commons health committee, and TV presenter Davina McCall all signed the letter.

'No opt-out'

It says: "We believe that all children and young people are entitled to receive sex and relationships education (SRE) as part of the statutory provision of personal, social, health and economic education (PSHE Education) in schools.

"No school should be able to opt out of delivering good sex and relationships education to their pupils (including primary schools, faith schools and academies), which should be taught throughout a pupil's time in education."

Young people would be handing over their own proposals on sex and relationship education to Schools Minister Jim Knight this week, the group said.

"We urge the government to listen to what they have to say."

In a statement, Mr Knight said parents did not have the right to withdraw their children from the statutory sex and education part of the curriculum, only the optional PHSE element.

Schools were teaching about the risks of unprotected sex and directing young people to local services where they could access contraceptive and sexual health advice, he added.

"Nevertheless, our teenage pregnancy strategy is working - teenage pregnancy rates are at their lowest for 20 years."